Breast cancer risk factors: Difference between revisions

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{{CMG}}
{{CMG}}
 
{{Breast cancer}}
==Overview==
==Overview==
==Risk Factors==
The primary risk factors that have been identified are sex,<ref name="Giordano">{{cite journal | last = Giordano | first = Sharon H | authorlink = | coauthors = Cohen DS, Buzdar AU, Perkins G, Hortobagyi GN | title = Breast carcinoma in men | journal = Cancer | volume = 101 | issue = 1 | pages = 51-57 | publisher =American Cancer Society | date = May 2004 | url= http://www3.interscience.wiley.com/cgi-bin/fulltext/108565241/HTMLSTART | doi = | id = | accessdate = }}</ref> age,<ref>{{cite web | title = Individual Risk Factors| publisher = BreastCancer.org | url = http://www.breastcancer.org/cmn_who_indrisk.html | accessdate = 2007-03-11}}</ref> childbearing, hormones,<ref>{{cite journal |author=Yager JD |coauthors=Davidson NE |title=Estrogen carcinogenesis in breast cancer |journal=New Engl J Med |volume=354 |issue=3 |year=2006 |pages=270-82 |id=PMID 16421368}}</ref> a high-fat diet,<ref>{{cite journal | author = Chlebowski RT, Blackburn GL, Thomson CA, Nixon DW, Shapiro A, Hoy MK, et al. | title = Dietary fat reduction and breast cancer outcome: interim efficacy results from the Women's Intervention Nutrition Study (WINS). | journal =J Natl Cancer Inst | volume =98 | issue =24 | pages =1767-1776 | pmid = 17179478 | url =}}</ref> alcohol intake,<ref name=Boffetta_2006>{{cite journal | last = Boffetta | first = Paolo | coauthors = Hashibe, Mia; La Vecchia, Carlo; Zatonski, Witold; Rehm, Jürgen | title = The burden of cancer attributable to alcohol drinking | journal = International Journal of Cancer | volume = 119 | issue = 4 | pages = 884–887 | publisher = Wiley-Liss, Inc | date = 2006-03-23 | url = http://www3.interscience.wiley.com/cgi-bin/abstract/112550783/ABSTRACT | doi = 10.1002/ijc.21903 | accessdate = 2006-10-09 | pmid=16557583 }}</ref> obesity,<ref>BBC report [http://news.bbc.co.uk/1/hi/health/5171838.stm Weight link to breast cancer risk]</ref> and environmental factors such as tobacco use and radiation.<ref name="acs bc facts 2005-6">{{cite web |author=[[American Cancer Society|ACS]] |year=2005 |title=Breast Cancer Facts & Figures 2005-2006 |url=http://www.cancer.org/downloads/STT/CAFF2005BrFacspdf2005.pdf |accessdate=2007-04-26}}</ref>
The primary risk factors that have been identified are sex,<ref name="Giordano">{{cite journal | last = Giordano | first = Sharon H | authorlink = | coauthors = Cohen DS, Buzdar AU, Perkins G, Hortobagyi GN | title = Breast carcinoma in men | journal = Cancer | volume = 101 | issue = 1 | pages = 51-57 | publisher =American Cancer Society | date = May 2004 | url= http://www3.interscience.wiley.com/cgi-bin/fulltext/108565241/HTMLSTART | doi = | id = | accessdate = }}</ref> age,<ref>{{cite web | title = Individual Risk Factors| publisher = BreastCancer.org | url = http://www.breastcancer.org/cmn_who_indrisk.html | accessdate = 2007-03-11}}</ref> childbearing, hormones,<ref>{{cite journal |author=Yager JD |coauthors=Davidson NE |title=Estrogen carcinogenesis in breast cancer |journal=New Engl J Med |volume=354 |issue=3 |year=2006 |pages=270-82 |id=PMID 16421368}}</ref> a high-fat diet,<ref>{{cite journal | author = Chlebowski RT, Blackburn GL, Thomson CA, Nixon DW, Shapiro A, Hoy MK, et al. | title = Dietary fat reduction and breast cancer outcome: interim efficacy results from the Women's Intervention Nutrition Study (WINS). | journal =J Natl Cancer Inst | volume =98 | issue =24 | pages =1767-1776 | pmid = 17179478 | url =}}</ref> alcohol intake,<ref name=Boffetta_2006>{{cite journal | last = Boffetta | first = Paolo | coauthors = Hashibe, Mia; La Vecchia, Carlo; Zatonski, Witold; Rehm, Jürgen | title = The burden of cancer attributable to alcohol drinking | journal = International Journal of Cancer | volume = 119 | issue = 4 | pages = 884–887 | publisher = Wiley-Liss, Inc | date = 2006-03-23 | url = http://www3.interscience.wiley.com/cgi-bin/abstract/112550783/ABSTRACT | doi = 10.1002/ijc.21903 | accessdate = 2006-10-09 | pmid=16557583 }}</ref> obesity,<ref>BBC report [http://news.bbc.co.uk/1/hi/health/5171838.stm Weight link to breast cancer risk]</ref> and environmental factors such as tobacco use and radiation.<ref name="acs bc facts 2005-6">{{cite web |author=[[American Cancer Society|ACS]] |year=2005 |title=Breast Cancer Facts & Figures 2005-2006 |url=http://www.cancer.org/downloads/STT/CAFF2005BrFacspdf2005.pdf |accessdate=2007-04-26}}</ref>


==Age==
===Age===
The risk of getting breast cancer increases with age. A woman who lives to age 90 has a lifetime risk of about 14.3%, or one in seven.<ref>{{cite web | title = Individual Risk Factors| publisher = BreastCander.org | url = http://www.breastcancer.org/cmn_who_indrisk.html | accessdate = 2007-03-11}}</ref> The probability of breast cancer rises with age, but breast cancer tends to be more aggressive when it occurs in younger people.  One type of breast cancer that is especially aggressive and that occurs disproportionately in younger people is [[inflammatory breast cancer]]. It is initially [[cancer staging|staged]] as Stage IIIb or Stage IV. It also is unique because it often does not present with a lump, so it is often undetected by [[mammography]] or [[medical ultrasonography|ultrasound]]. It presents with the signs and symptoms of a breast infection like [[mastitis]], and the treatment is usually a combination of surgery, radiation, and chemotherapy.
The risk of getting breast cancer increases with age. A woman who lives to age 90 has a lifetime risk of about 14.3%, or one in seven.<ref>{{cite web | title = Individual Risk Factors| publisher = BreastCander.org | url = http://www.breastcancer.org/cmn_who_indrisk.html | accessdate = 2007-03-11}}</ref> The probability of breast cancer rises with age, but breast cancer tends to be more aggressive when it occurs in younger people.  One type of breast cancer that is especially aggressive and that occurs disproportionately in younger people is [[inflammatory breast cancer]]. It is initially [[cancer staging|staged]] as Stage IIIb or Stage IV. It also is unique because it often does not present with a lump, so it is often undetected by [[mammography]] or [[medical ultrasonography|ultrasound]]. It presents with the signs and symptoms of a breast infection like [[mastitis]], and the treatment is usually a combination of surgery, radiation, and chemotherapy.


==Sex==
===Sex===
Men have a lower risk of developing breast cancer (approximately 1.08 per 100,000 men per year), but this risk appears to be rising.<ref name="Giordano">{{cite journal | last = Giordano | first = Sharon H | authorlink = | coauthors = Cohen DS, Buzdar AU, Perkins G, Hortobagyi GN | title = Breast carcinoma in men | journal = Cancer | volume = 101 | issue = 1 | pages = 51-57 | publisher =American Cancer Society | date = May 2004 | url= http://www3.interscience.wiley.com/cgi-bin/fulltext/108565241/HTMLSTART | doi = | id = | accessdate = }}</ref>
Men have a lower risk of developing breast cancer (approximately 1.08 per 100,000 men per year), but this risk appears to be rising.<ref name="Giordano">{{cite journal | last = Giordano | first = Sharon H | authorlink = | coauthors = Cohen DS, Buzdar AU, Perkins G, Hortobagyi GN | title = Breast carcinoma in men | journal = Cancer | volume = 101 | issue = 1 | pages = 51-57 | publisher =American Cancer Society | date = May 2004 | url= http://www3.interscience.wiley.com/cgi-bin/fulltext/108565241/HTMLSTART | doi = | id = | accessdate = }}</ref>


==Heredity==
===Heredity===
In 5% of breast cancer cases, there is a strong inherited familial risk.<ref name="pmid9544766">{{cite journal |author=Malone KE, Daling JR, Thompson JD, O'Brien CA, Francisco LV, Ostrander EA |title=BRCA1 mutations and breast cancer in the general population: analyses in women before age 35 years and in women before age 45 years with first-degree family history |journal=JAMA |volume=279 |issue=12 |pages=922-9 |year=1998 |pmid=9544766 |doi=}}</ref>  
In 5% of breast cancer cases, there is a strong inherited familial risk.<ref name="pmid9544766">{{cite journal |author=Malone KE, Daling JR, Thompson JD, O'Brien CA, Francisco LV, Ostrander EA |title=BRCA1 mutations and breast cancer in the general population: analyses in women before age 35 years and in women before age 45 years with first-degree family history |journal=JAMA |volume=279 |issue=12 |pages=922-9 |year=1998 |pmid=9544766 |doi=}}</ref>  
Two autosomal dominant [[gene]]s, ''[[BRCA1]]'' and ''[[BRCA2]]'', account for most of the cases of familial breast cancer. Family members who harbor mutations in these genes have a 60% to 80% risk of developing breast cancer in their lifetimes.<ref name="pmid9544766"/>  Other associated malignancies include [[ovarian cancer]] and [[pancreatic cancer]]. If a mother or a sister was diagnosed breast cancer, the risk of a hereditary ‘’’[[BRCA1]]’’’ or ‘’’[[BRCA2]]’’’ gene mutation is about 2-fold higher than those women without a familial history.  In addition to the BRCA genes associated with breast cancer, the presence of ''[[NBR2]]'', near breast cancer gene 1, has been discovered, and research into its contribution to breast cancer pathogenesis is ongoing.<ref name="Beth Elton_2007">{{cite journal |author=Emilie Auriol, Lise-Marie Billard, Frederique Magdinier, Robert Dante |title=Specific binding of the methyl binding domain protein 2 at the ''BRCA1-NBR2'' locus |journal=Nucleic Acids Research |volume=33 |issue=13 |pages=4243-4254 |year=2005}}</ref>
Two autosomal dominant [[gene]]s, ''[[BRCA1]]'' and ''[[BRCA2]]'', account for most of the cases of familial breast cancer. Family members who harbor mutations in these genes have a 60% to 80% risk of developing breast cancer in their lifetimes.<ref name="pmid9544766"/>  Other associated malignancies include [[ovarian cancer]] and [[pancreatic cancer]]. If a mother or a sister was diagnosed breast cancer, the risk of a hereditary ‘’’[[BRCA1]]’’’ or ‘’’[[BRCA2]]’’’ gene mutation is about 2-fold higher than those women without a familial history.  In addition to the BRCA genes associated with breast cancer, the presence of ''[[NBR2]]'', near breast cancer gene 1, has been discovered, and research into its contribution to breast cancer pathogenesis is ongoing.<ref name="Beth Elton_2007">{{cite journal |author=Emilie Auriol, Lise-Marie Billard, Frederique Magdinier, Robert Dante |title=Specific binding of the methyl binding domain protein 2 at the ''BRCA1-NBR2'' locus |journal=Nucleic Acids Research |volume=33 |issue=13 |pages=4243-4254 |year=2005}}</ref>
Commercial testing for ‘’’[[BRCA1]]’’’ and ‘’’[[BRCA2]]’’’ gene mutations has been available since at least 2004.  Genetic testing for BRCA gene mutations is conducted exclusively by [[Myriad Genetics]], located in Salt Lake City.
Commercial testing for ‘’’[[BRCA1]]’’’ and ‘’’[[BRCA2]]’’’ gene mutations has been available since at least 2004.  Genetic testing for BRCA gene mutations is conducted exclusively by [[Myriad Genetics]], located in Salt Lake City.


==Diet==
===Diet===
Dietary influences have been proposed and examined, and recent research suggests that low-fat diets may significantly decrease the risk of breast cancer as well as the recurrence of breast cancer.<ref>{{cite journal
Dietary influences have been proposed and examined, and recent research suggests that low-fat diets may significantly decrease the risk of breast cancer as well as the recurrence of breast cancer.<ref>{{cite journal
   | author = Chlebowski RT, Blackburn GL, Thomson CA, Nixon DW, Shapiro A, Hoy MK, et al.  
   | author = Chlebowski RT, Blackburn GL, Thomson CA, Nixon DW, Shapiro A, Hoy MK, et al.  
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A significant environmental effect is likely responsible for the different rates of breast cancer incidence between countries with different dietary customs.  Researchers have long measured that breast cancer rates in an immigrant population soon come to resemble the rates of the host country after a few generations.  The reason for this is speculated to be immigrant uptake of the host country diet.  The prototypical example of this phenomenon is the changing rate of breast cancer after the arrival of Japanese immigrants to America.<ref>{{cite journal |author= Nelson N title = Migrant Studies Aid Search for Factors Linked to Breast Cancer Risk |journal=JAMA |volume=8 |issue=7 |pages=436-438 |year=2006}}</ref>
A significant environmental effect is likely responsible for the different rates of breast cancer incidence between countries with different dietary customs.  Researchers have long measured that breast cancer rates in an immigrant population soon come to resemble the rates of the host country after a few generations.  The reason for this is speculated to be immigrant uptake of the host country diet.  The prototypical example of this phenomenon is the changing rate of breast cancer after the arrival of Japanese immigrants to America.<ref>{{cite journal |author= Nelson N title = Migrant Studies Aid Search for Factors Linked to Breast Cancer Risk |journal=JAMA |volume=8 |issue=7 |pages=436-438 |year=2006}}</ref>


==Alcohol Consumption==
===Alcohol Consumption===
Alcohol appears to increase the risk of breast cancer, though meaningful increases are limited to higher alcohol intake levels. Breast cancer constitutes about 7.3% of all cancers.<ref name=ACS_2007>{{cite web | title = Statistics for 2007 | publisher = American Cancer Society | url = http://www.cancer.org/docroot/stt/stt_0.asp | accessdate = 2007-03-11}}</ref> Among women, breast cancer comprises 60% of alcohol-attributable cancers.<ref name=Boffetta_2006>{{cite journal
Alcohol appears to increase the risk of breast cancer, though meaningful increases are limited to higher alcohol intake levels. Breast cancer constitutes about 7.3% of all cancers.<ref name=ACS_2007>{{cite web | title = Statistics for 2007 | publisher = American Cancer Society | url = http://www.cancer.org/docroot/stt/stt_0.asp | accessdate = 2007-03-11}}</ref> Among women, breast cancer comprises 60% of alcohol-attributable cancers.<ref name=Boffetta_2006>{{cite journal
   | last = Boffetta
   | last = Boffetta
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"Folate intake counteracts breast cancer risk associated with alcohol consumption"<ref>Mayo Clinic news release [[June 26]] 2001 [http://www.mayoclinic.org/news2001-rst/857.html "Folate Intake Counteracts Breast Cancer Risk Associated with Alcohol Consumption"]</ref> and "women who drink alcohol and have a high folate intake are not at increased risk of cancer."<ref>Boston University [http://www.bu.edu/act/alcoholandhealth/issues/issue_may04/html/04-0506-ellison_baily.html ''Folate, Alcohol, and Cancer Risk'']</ref> Those who have a high (200 micrograms or more per day) level of [[folate]] (folic acid or Vitamin B9) in their diet are not at increased risk of breast cancer compared to those who abstain from alcohol.<ref name=Zhang_1999>{{cite journal |author=Zhang S, Hunter D, Hankinson S, Giovannucci E, Rosner B, Colditz G, Speizer F, Willett W |title=A prospective study of folate intake and the risk of breast cancer |journal=JAMA |volume=281 |issue=17 |pages=1632-7 |year=1999 |pmid=10235158}}</ref> Foods rich in folate include citrus fruits, citrus juices, dark green leafy vegetables (such as spinach), dried beans, and peas. Vitamin B9 can also be taken in a multivitamin pill.
"Folate intake counteracts breast cancer risk associated with alcohol consumption"<ref>Mayo Clinic news release [[June 26]] 2001 [http://www.mayoclinic.org/news2001-rst/857.html "Folate Intake Counteracts Breast Cancer Risk Associated with Alcohol Consumption"]</ref> and "women who drink alcohol and have a high folate intake are not at increased risk of cancer."<ref>Boston University [http://www.bu.edu/act/alcoholandhealth/issues/issue_may04/html/04-0506-ellison_baily.html ''Folate, Alcohol, and Cancer Risk'']</ref> Those who have a high (200 micrograms or more per day) level of [[folate]] (folic acid or Vitamin B9) in their diet are not at increased risk of breast cancer compared to those who abstain from alcohol.<ref name=Zhang_1999>{{cite journal |author=Zhang S, Hunter D, Hankinson S, Giovannucci E, Rosner B, Colditz G, Speizer F, Willett W |title=A prospective study of folate intake and the risk of breast cancer |journal=JAMA |volume=281 |issue=17 |pages=1632-7 |year=1999 |pmid=10235158}}</ref> Foods rich in folate include citrus fruits, citrus juices, dark green leafy vegetables (such as spinach), dried beans, and peas. Vitamin B9 can also be taken in a multivitamin pill.


==Obesity==
===Obesity===
Gaining weight after menopause can increase a woman's risk. A recent study found that putting on 9.9kg (22lbs) after menopause increased the risk of developing breast cancer by 18%.<ref>BBC report [http://news.bbc.co.uk/1/hi/health/5171838.stm Weight link to breast cancer risk]</ref>
Gaining weight after menopause can increase a woman's risk. A recent study found that putting on 9.9kg (22lbs) after menopause increased the risk of developing breast cancer by 18%.<ref>BBC report [http://news.bbc.co.uk/1/hi/health/5171838.stm Weight link to breast cancer risk]</ref>


==Hormones==
===Hormones===
Persistently increased blood levels of [[estrogen]] are associated with an increased risk of breast cancer, as are increased levels of the [[androgens]] [[androstenedione]] and [[testosterone]] (which can be directly converted by [[aromatase]] to the estrogens [[estrone]] and [[estradiol]], respectively). Increased blood levels of [[progesterone]] are associated with a decreased risk of breast cancer in premenopausal women.<ref>{{cite journal |author=Yager JD |coauthors=Davidson NE |title=Estrogen carcinogenesis in breast cancer |journal=New Engl J Med |volume=354 |issue=3 |year=2006 |pages=270-82 |id=PMID 16421368}}</ref> A number of circumstances which increase exposure to endogenous estrogens including not having children, delaying first childbirth, not breastfeeding, early [[menarche]] (the first menstrual period) and late [[menopause]] are suspected of increasing lifetime risk for developing breast cancer.<ref>American Cancer Society. ([[2006-10-03]]). [http://www.cancer.org/docroot/CRI/content/CRI_2_4_2X_What_are_the_risk_factors_for_breast_cancer_5.asp What Are the Risk Factors for Breast Cancer?] Retrieved [[2006-03-30]].</ref>
Persistently increased blood levels of [[estrogen]] are associated with an increased risk of breast cancer, as are increased levels of the [[androgens]] [[androstenedione]] and [[testosterone]] (which can be directly converted by [[aromatase]] to the estrogens [[estrone]] and [[estradiol]], respectively). Increased blood levels of [[progesterone]] are associated with a decreased risk of breast cancer in premenopausal women.<ref>{{cite journal |author=Yager JD |coauthors=Davidson NE |title=Estrogen carcinogenesis in breast cancer |journal=New Engl J Med |volume=354 |issue=3 |year=2006 |pages=270-82 |id=PMID 16421368}}</ref> A number of circumstances which increase exposure to endogenous estrogens including not having children, delaying first childbirth, not breastfeeding, early [[menarche]] (the first menstrual period) and late [[menopause]] are suspected of increasing lifetime risk for developing breast cancer.<ref>American Cancer Society. ([[2006-10-03]]). [http://www.cancer.org/docroot/CRI/content/CRI_2_4_2X_What_are_the_risk_factors_for_breast_cancer_5.asp What Are the Risk Factors for Breast Cancer?] Retrieved [[2006-03-30]].</ref>


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Data exist from both observational and [[randomized clinical trial]]s regarding the association between postmenopausal [[hormone replacement therapy]] (HRT) and breast cancer. The largest meta-analysis (1997) of data from 51 observational studies, indicated a relative risk of breast cancer of 1.35 for women who had used HRT for 5 or more years after menopause. The estrogen-plus-[[progestin]] arm of the [[Women's Health Initiative]] (WHI), a randomized controlled trial, which randomized more than 16,000 postmenopausal women to receive combined hormone therapy or placebo, was halted early (2002) because health risks exceeded benefits. One of the adverse outcomes prompting closure was a significant increase in both total and invasive breast cancers (RR = 1.24) in women randomized to receive estrogen and progestin for an average of 5 years. HRT-related breast cancers had adverse prognostic characteristics (more advanced stages and larger tumors) compared with cancers occurring in the placebo group, and HRT was also associated with a substantial increase in abnormal mammograms. Short-term use of hormones for treatment of menopausal symptoms appears to confer little or no breast cancer risk.<ref name=hormone>{{cite web |url=http://www.cancer.gov/cancertopics/pdq/genetics/breast-and-ovarian/healthprofessional#Section_340 |title=Hormone Therapy |accessdate=2006-08-12 |author=National Cancer Institute |date=2006-08-03 |work=Genetics of Breast and Ovarian Cancer}}</ref>
Data exist from both observational and [[randomized clinical trial]]s regarding the association between postmenopausal [[hormone replacement therapy]] (HRT) and breast cancer. The largest meta-analysis (1997) of data from 51 observational studies, indicated a relative risk of breast cancer of 1.35 for women who had used HRT for 5 or more years after menopause. The estrogen-plus-[[progestin]] arm of the [[Women's Health Initiative]] (WHI), a randomized controlled trial, which randomized more than 16,000 postmenopausal women to receive combined hormone therapy or placebo, was halted early (2002) because health risks exceeded benefits. One of the adverse outcomes prompting closure was a significant increase in both total and invasive breast cancers (RR = 1.24) in women randomized to receive estrogen and progestin for an average of 5 years. HRT-related breast cancers had adverse prognostic characteristics (more advanced stages and larger tumors) compared with cancers occurring in the placebo group, and HRT was also associated with a substantial increase in abnormal mammograms. Short-term use of hormones for treatment of menopausal symptoms appears to confer little or no breast cancer risk.<ref name=hormone>{{cite web |url=http://www.cancer.gov/cancertopics/pdq/genetics/breast-and-ovarian/healthprofessional#Section_340 |title=Hormone Therapy |accessdate=2006-08-12 |author=National Cancer Institute |date=2006-08-03 |work=Genetics of Breast and Ovarian Cancer}}</ref>


==Environmental risk factors==
===Environmental risk factors===
===Tobacco===
====Tobacco====
Most studies have not found an increased risk of breast cancer from active [[tobacco smoking]], although a number of studies suggest an increased risk of breast cancer in both active smokers and those exposed to [[passive smoking|secondhand smoke]] compared to women who reported no exposure to secondhand smoke.<ref name="acs bc facts 2005-6"/>
Most studies have not found an increased risk of breast cancer from active [[tobacco smoking]], although a number of studies suggest an increased risk of breast cancer in both active smokers and those exposed to [[passive smoking|secondhand smoke]] compared to women who reported no exposure to secondhand smoke.<ref name="acs bc facts 2005-6"/>


===Radiation===
====Radiation====
Women who have received high-dose [[ionizing radiation]] to the chest (for example, as treatments for other cancers) have a relative risk of breast cancer between 2.1 to 4.0.<!--
Women who have received high-dose [[ionizing radiation]] to the chest (for example, as treatments for other cancers) have a relative risk of breast cancer between 2.1 to 4.0.<!--
   --><ref name="acs bc facts 2005-6">{{cite web |author=[[American Cancer Society|ACS]] |year=2005 |title=Breast Cancer Facts & Figures 2005-2006 |url=http://www.cancer.org/downloads/STT/CAFF2005BrFacspdf2005.pdf |accessdate=2007-04-26}}</ref>
   --><ref name="acs bc facts 2005-6">{{cite web |author=[[American Cancer Society|ACS]] |year=2005 |title=Breast Cancer Facts & Figures 2005-2006 |url=http://www.cancer.org/downloads/STT/CAFF2005BrFacspdf2005.pdf |accessdate=2007-04-26}}</ref>


===Impact of environmental estrogenic mimics===
====Impact of environmental estrogenic mimics====
Although environmental exposures are not generally cited as risk factors for the disease (except for diet, pharmaceuticals and radiation), a substantial and growing body of evidence indicates that exposures to certain toxic chemicals and hormone-mimicking compounds including chemicals used in pesticides, cosmetics and cleaning products contribute to the development of breast cancer.
Although environmental exposures are not generally cited as risk factors for the disease (except for diet, pharmaceuticals and radiation), a substantial and growing body of evidence indicates that exposures to certain toxic chemicals and hormone-mimicking compounds including chemicals used in pesticides, cosmetics and cleaning products contribute to the development of breast cancer.
A recent Canadian study concluded that female farm workers are three times more likely to have breast cancer.<ref>{{cite news | author = Ctv.Ca News Staff | title= Breast cancer more likely in farm workers: study |url= http://www.ctv.ca/servlet/ArticleNews/story/CTVNews/20061012/breastcancer_farming_061012/20061012?hub=Health| publisher= Ctv.Ca |date=2006-10-12 |accessdate=2007-03-11 }}</ref>
A recent Canadian study concluded that female farm workers are three times more likely to have breast cancer.<ref>{{cite news | author = Ctv.Ca News Staff | title= Breast cancer more likely in farm workers: study |url= http://www.ctv.ca/servlet/ArticleNews/story/CTVNews/20061012/breastcancer_farming_061012/20061012?hub=Health| publisher= Ctv.Ca |date=2006-10-12 |accessdate=2007-03-11 }}</ref>
The increasing prevalence of these substances in the environment may explain the increasing incidence of breast cancer, though direct evidence is sparse.
The increasing prevalence of these substances in the environment may explain the increasing incidence of breast cancer, though direct evidence is sparse.


===Dioxins===
====Dioxins====
Although not well-quantified, there has long been a concern about risk associated with environmental estrogenic compounds, such as [[dioxins]]. {{Fact|date=June 2007}}
Although not well-quantified, there has long been a concern about risk associated with environmental estrogenic compounds, such as [[dioxins]]. {{Fact|date=June 2007}}


===Light levels===
====Light levels====
Researchers at the [[National Cancer Institute]] and [[National Institute of Environmental Health Sciences]] have concluded a study that suggests that artificial light during the night can be a factor for breast cancer.<ref>''The Independent'' [http://news.independent.co.uk/uk/health_medical/article1090208.ece Avoid breast cancer. Sleep in the dark...]</ref>
Researchers at the [[National Cancer Institute]] and [[National Institute of Environmental Health Sciences]] have concluded a study that suggests that artificial light during the night can be a factor for breast cancer.<ref>''The Independent'' [http://news.independent.co.uk/uk/health_medical/article1090208.ece Avoid breast cancer. Sleep in the dark...]</ref>


==Viral breast cancer pathogenesis research==
===Viral breast cancer pathogenesis research===
Humans are not the only mammals susceptible to breast cancer.  Some strains of mice, namely the house mouse (Mus domesticus) are prone to breast cancer which is caused by infection with the [[mouse mammary tumour virus]] (MMTV or "Bittner virus" for its discoverer Hans Bittner), by random insertional mutagenesis.  This finding is taken to mean that a viral [[etiology]] of human breast cancer is at least possible, though there is no definitive evidence to support the claim that MMTV causes human breast cancer.  For example, there may be critical differences between cancer pathogenesis in mice and people.  The understanding of the role of MMTV or other viruses in human breast cancer is preliminary as of May 2007.
Humans are not the only mammals susceptible to breast cancer.  Some strains of mice, namely the house mouse (Mus domesticus) are prone to breast cancer which is caused by infection with the [[mouse mammary tumour virus]] (MMTV or "Bittner virus" for its discoverer Hans Bittner), by random insertional mutagenesis.  This finding is taken to mean that a viral [[etiology]] of human breast cancer is at least possible, though there is no definitive evidence to support the claim that MMTV causes human breast cancer.  For example, there may be critical differences between cancer pathogenesis in mice and people.  The understanding of the role of MMTV or other viruses in human breast cancer is preliminary as of May 2007.


==Factors with minimal or no impact on breast cancer risk==
===Factors with minimal or no impact on breast cancer risk===
===Abortion===
====Abortion====
Studies in rats<ref name="RUSSO3">{{cite journal |author=Russo J, Russo I |title=Biological and molecular bases of mammary carcinogenesis |journal=Lab Invest |volume=57 |issue=2 |pages=112-37 |year=1987 |pmid=3302534}}</ref> led to speculation that [[abortion]] may increase the risk of breast cancer because of hormones initiating breast tissue growth in early pregnancy. Some early interview<ref name="DALING">Daling J.R. ''et al.'' (1994) [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=7932822 PubMed] ''Risk of breast cancer among young women: relationship to induced abortion.'' J Natl Cancer Inst. 1994 Nov 2;86(21):1584-92.</ref> and record<ref name="HOWE">{{cite journal | author = Howe H, Senie R, Bzduch H, Herzfeld P | title = Early abortion and breast cancer risk among women under age 40. | journal = Int J Epidemiol | volume = 18 | issue = 2 | pages = 300-4 | year = 1989 | id = PMID 2767842}}</ref> based [[case-control]] studies indicated a possible correlation, but more recent record based studies<ref name="MELBYE">{{cite journal |author=Melbye M, Wohlfahrt J, Olsen J, Frisch M, Westergaard T, Helweg-Larsen K, Andersen P |title=Induced abortion and the risk of breast cancer |journal=N Engl J Med |volume=336 |issue=2 |pages=81-5 |year=1997 |pmid=8988884}}</ref><ref name="epic">{{cite journal |author=Reeves G, Kan S, Key T, Tjønneland A, Olsen A, Overvad K, Peeters P, Clavel-Chapelon F, Paoletti X, Berrino F, Krogh V, Palli D, Tumino R, Panico S, Vineis P, Gonzalez C, Ardanaz E, Martinez C, Amiano P, Quiros J, Tormo M, Khaw K, Trichopoulou A, Psaltopoulou T, Kalapothaki V, Nagel G, Chang-Claude J, Boeing H, Lahmann P, Wirfält E, Kaaks R, Riboli E |title=Breast cancer risk in relation to abortion: Results from the EPIC study |journal=Int. J. Cancer |volume=119 |issue=7 |pages=1741-5 |year=2006 |pmid=16646050}}</ref><ref name="harvard">Karin B. Michels, ScD, PhD; Fei Xue, MD; Graham A. Colditz, MD, DrPH; Walter C. Willett, MD, DrPH. "Induced and Spontaneous Abortion and Incidence of Breast Cancer Among Young Women." ''Arch Intern Med.'' 2007;167:814-820. [http://archinte.ama-assn.org/cgi/content/short/167/8/814 Abstract].</ref> and a large [[meta-analysis]]<ref>Beral V, Bull D et al, "Breast cancer and abortion: collaborative reanalysis of data from 53 epidemiological studies, including 83,000 women with breast cancer from 16 countries." ''Lancet,'' 2004 Mar 27;363(9414):1007-16 [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?itool=abstractplus&db=pubmed&cmd=Retrieve&dopt=abstractplus&list_uids=15051280 PMID 15051280]</ref> study do not support this association. The subject was examined by a [[National Cancer Institute]] (NCI) workshop in 2003, in response to the Bush Administration's alteration of the NCI's website to emphasize studies indicating a potential link.<ref>[http://oversight.house.gov/features/politics_and_science/example_breast_cancer.htm Politics and Science: Breast Cancer Risk]. Accessed [[July 23]] [[2007]].</ref> The NCI expert panel concluded, with the strongest level of evidence, that induced abortion is not associated with an increased breast cancer risk.<ref>[http://www.cancer.gov/cancerinfo/ere-workshop-report Summary Report: Early Reproductive Events and Breast Cancer Workshop], from the U.S. [[National Cancer Institute]]. Posted [[March 4]] [[2003]]; accessed [[July 23]] [[2007]].</ref>
Studies in rats<ref name="RUSSO3">{{cite journal |author=Russo J, Russo I |title=Biological and molecular bases of mammary carcinogenesis |journal=Lab Invest |volume=57 |issue=2 |pages=112-37 |year=1987 |pmid=3302534}}</ref> led to speculation that [[abortion]] may increase the risk of breast cancer because of hormones initiating breast tissue growth in early pregnancy. Some early interview<ref name="DALING">Daling J.R. ''et al.'' (1994) [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=7932822 PubMed] ''Risk of breast cancer among young women: relationship to induced abortion.'' J Natl Cancer Inst. 1994 Nov 2;86(21):1584-92.</ref> and record<ref name="HOWE">{{cite journal | author = Howe H, Senie R, Bzduch H, Herzfeld P | title = Early abortion and breast cancer risk among women under age 40. | journal = Int J Epidemiol | volume = 18 | issue = 2 | pages = 300-4 | year = 1989 | id = PMID 2767842}}</ref> based [[case-control]] studies indicated a possible correlation, but more recent record based studies<ref name="MELBYE">{{cite journal |author=Melbye M, Wohlfahrt J, Olsen J, Frisch M, Westergaard T, Helweg-Larsen K, Andersen P |title=Induced abortion and the risk of breast cancer |journal=N Engl J Med |volume=336 |issue=2 |pages=81-5 |year=1997 |pmid=8988884}}</ref><ref name="epic">{{cite journal |author=Reeves G, Kan S, Key T, Tjønneland A, Olsen A, Overvad K, Peeters P, Clavel-Chapelon F, Paoletti X, Berrino F, Krogh V, Palli D, Tumino R, Panico S, Vineis P, Gonzalez C, Ardanaz E, Martinez C, Amiano P, Quiros J, Tormo M, Khaw K, Trichopoulou A, Psaltopoulou T, Kalapothaki V, Nagel G, Chang-Claude J, Boeing H, Lahmann P, Wirfält E, Kaaks R, Riboli E |title=Breast cancer risk in relation to abortion: Results from the EPIC study |journal=Int. J. Cancer |volume=119 |issue=7 |pages=1741-5 |year=2006 |pmid=16646050}}</ref><ref name="harvard">Karin B. Michels, ScD, PhD; Fei Xue, MD; Graham A. Colditz, MD, DrPH; Walter C. Willett, MD, DrPH. "Induced and Spontaneous Abortion and Incidence of Breast Cancer Among Young Women." ''Arch Intern Med.'' 2007;167:814-820. [http://archinte.ama-assn.org/cgi/content/short/167/8/814 Abstract].</ref> and a large [[meta-analysis]]<ref>Beral V, Bull D et al, "Breast cancer and abortion: collaborative reanalysis of data from 53 epidemiological studies, including 83,000 women with breast cancer from 16 countries." ''Lancet,'' 2004 Mar 27;363(9414):1007-16 [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?itool=abstractplus&db=pubmed&cmd=Retrieve&dopt=abstractplus&list_uids=15051280 PMID 15051280]</ref> study do not support this association. The subject was examined by a [[National Cancer Institute]] (NCI) workshop in 2003, in response to the Bush Administration's alteration of the NCI's website to emphasize studies indicating a potential link.<ref>[http://oversight.house.gov/features/politics_and_science/example_breast_cancer.htm Politics and Science: Breast Cancer Risk]. Accessed [[July 23]] [[2007]].</ref> The NCI expert panel concluded, with the strongest level of evidence, that induced abortion is not associated with an increased breast cancer risk.<ref>[http://www.cancer.gov/cancerinfo/ere-workshop-report Summary Report: Early Reproductive Events and Breast Cancer Workshop], from the U.S. [[National Cancer Institute]]. Posted [[March 4]] [[2003]]; accessed [[July 23]] [[2007]].</ref>


===Deodorants===
====Deodorants====
Much has been made of the possible contribution of aluminum-containing underarm antiperspirants to the incidence of breast cancer, since the most common location of a breast cancer is the upper outer quadrant of the breast.  [[Aluminum]] salts, such as those used in anti-perspirants, have recently been classified as metalloestrogens. In research published in the ''Journal of Applied Toxicology'', Dr. Philippa D. Darbre of the University of Reading has shown that aluminum salts increase estrogen-related gene expression in human breast cancer cells grown in the laboratory.<ref>Harding, Anne. (2006) [http://www.cancerpage.com/news/article.asp?id=9466 Aluminum Salts Could Increase Breast Cancer Risk]. Reuters Health.</ref><ref>{{cite journal
Much has been made of the possible contribution of aluminum-containing underarm antiperspirants to the incidence of breast cancer, since the most common location of a breast cancer is the upper outer quadrant of the breast.  [[Aluminum]] salts, such as those used in anti-perspirants, have recently been classified as metalloestrogens. In research published in the ''Journal of Applied Toxicology'', Dr. Philippa D. Darbre of the University of Reading has shown that aluminum salts increase estrogen-related gene expression in human breast cancer cells grown in the laboratory.<ref>Harding, Anne. (2006) [http://www.cancerpage.com/news/article.asp?id=9466 Aluminum Salts Could Increase Breast Cancer Risk]. Reuters Health.</ref><ref>{{cite journal
   | last =Darbre  
   | last =Darbre  
Line 123: Line 125:
Fortunately, this ''in-vitro'' association between aluminum salts and estrogen activity does not translate into an increased risk of breast cancer in humans. The lack of association between underarm deodorants and breast cancer has been the subject of a number of research articles.<ref name="pmid14991030">{{cite journal |author=Surendran A |title=Studies linking breast cancer to deodorants smell rotten, experts say |journal=Nat. Med. |volume=10 |issue=3 |pages=216 |year=2004 |pmid=14991030 |doi=10.1038/nm0304-216b}}</ref><ref name="pmid12543590">{{cite journal |author= |title=Antiperspirants don't cause breast cancer |journal=Harvard women's health watch |volume=10 |issue=5 |pages=7 |year=2003 |pmid=12543590 |doi=}}</ref>
Fortunately, this ''in-vitro'' association between aluminum salts and estrogen activity does not translate into an increased risk of breast cancer in humans. The lack of association between underarm deodorants and breast cancer has been the subject of a number of research articles.<ref name="pmid14991030">{{cite journal |author=Surendran A |title=Studies linking breast cancer to deodorants smell rotten, experts say |journal=Nat. Med. |volume=10 |issue=3 |pages=216 |year=2004 |pmid=14991030 |doi=10.1038/nm0304-216b}}</ref><ref name="pmid12543590">{{cite journal |author= |title=Antiperspirants don't cause breast cancer |journal=Harvard women's health watch |volume=10 |issue=5 |pages=7 |year=2003 |pmid=12543590 |doi=}}</ref>


===Fertility treatments===
====Fertility treatments====
There is no persuasive connection between fertility medications and breast cancer.<ref>{{cite journal |author=Potashnik G, Lerner-Geva L, Genkin L, Chetrit A, Lunenfeld E, Porath A |title=Fertility drugs and the risk of breast and ovarian cancers: results of a long-term follow-up study |journal=Fertil. Steril. |volume=71 |issue=5 |pages=853-9 |year=1999 |pmid=10231045 |doi=}}</ref>
There is no persuasive connection between fertility medications and breast cancer.<ref>{{cite journal |author=Potashnik G, Lerner-Geva L, Genkin L, Chetrit A, Lunenfeld E, Porath A |title=Fertility drugs and the risk of breast and ovarian cancers: results of a long-term follow-up study |journal=Fertil. Steril. |volume=71 |issue=5 |pages=853-9 |year=1999 |pmid=10231045 |doi=}}</ref>
==References==
==References==
{{Reflist|2}}
{{Reflist|2}}
[[Category:Disease]]
[[Category:Types of cancer]]
[[Category:Breast]]
[[Category:Hereditary cancers]]
[[Category:Oncology]]
[[Category:Mature chapter]]


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{{WH}}
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Overview

Risk Factors

The primary risk factors that have been identified are sex,[1] age,[2] childbearing, hormones,[3] a high-fat diet,[4] alcohol intake,[5] obesity,[6] and environmental factors such as tobacco use and radiation.[7]

Age

The risk of getting breast cancer increases with age. A woman who lives to age 90 has a lifetime risk of about 14.3%, or one in seven.[8] The probability of breast cancer rises with age, but breast cancer tends to be more aggressive when it occurs in younger people. One type of breast cancer that is especially aggressive and that occurs disproportionately in younger people is inflammatory breast cancer. It is initially staged as Stage IIIb or Stage IV. It also is unique because it often does not present with a lump, so it is often undetected by mammography or ultrasound. It presents with the signs and symptoms of a breast infection like mastitis, and the treatment is usually a combination of surgery, radiation, and chemotherapy.

Sex

Men have a lower risk of developing breast cancer (approximately 1.08 per 100,000 men per year), but this risk appears to be rising.[1]

Heredity

In 5% of breast cancer cases, there is a strong inherited familial risk.[9] Two autosomal dominant genes, BRCA1 and BRCA2, account for most of the cases of familial breast cancer. Family members who harbor mutations in these genes have a 60% to 80% risk of developing breast cancer in their lifetimes.[9] Other associated malignancies include ovarian cancer and pancreatic cancer. If a mother or a sister was diagnosed breast cancer, the risk of a hereditary ‘’’BRCA1’’’ or ‘’’BRCA2’’’ gene mutation is about 2-fold higher than those women without a familial history. In addition to the BRCA genes associated with breast cancer, the presence of NBR2, near breast cancer gene 1, has been discovered, and research into its contribution to breast cancer pathogenesis is ongoing.[10] Commercial testing for ‘’’BRCA1’’’ and ‘’’BRCA2’’’ gene mutations has been available since at least 2004. Genetic testing for BRCA gene mutations is conducted exclusively by Myriad Genetics, located in Salt Lake City.

Diet

Dietary influences have been proposed and examined, and recent research suggests that low-fat diets may significantly decrease the risk of breast cancer as well as the recurrence of breast cancer.[11] Another study showed no contribution of dietary fat intake on the incidence of breast cancer in over 300,000 women.[12] A randomized controlled study of the consequences of a low-fat diet, the Women's Health Initiative, failed to show a statistically significant reduction in breast cancer incidence in the group assigned to a low-fat diet, although the authors did find evidence of a benefit in the subgoup of women who followed the low-fat diet in a strict manner.[13] Another randomized trial, the Nurses' Health Study II, found increased breast cancer incidence in premenopausal women only, with higher intake of animal fat, but not vegetable fat. Taken as a whole, these results point to a possible association between dietary fat intake and breast cancer incidence, though these interactions are hard to measure in large groups of women.

In a study published in the Journal of the American Medical Association, biomedical investigators found that Brassica vegetable intake (broccoli, cauliflower, cabbage, kale and Brussels sprouts) was inversely related to breast cancer development. The relative risk among women in the highest decile of Brassica vegetable consumption (median, 1.5 servings per day) compared to the lowest decile (virtually no consumption) was 58%. That is, women who consumed the most Brassica vegetables were 58% less likely to develop breast cancer.[14]

A significant environmental effect is likely responsible for the different rates of breast cancer incidence between countries with different dietary customs. Researchers have long measured that breast cancer rates in an immigrant population soon come to resemble the rates of the host country after a few generations. The reason for this is speculated to be immigrant uptake of the host country diet. The prototypical example of this phenomenon is the changing rate of breast cancer after the arrival of Japanese immigrants to America.[15]

Alcohol Consumption

Alcohol appears to increase the risk of breast cancer, though meaningful increases are limited to higher alcohol intake levels. Breast cancer constitutes about 7.3% of all cancers.[16] Among women, breast cancer comprises 60% of alcohol-attributable cancers.[5] The UK's Review of Alcohol: Association with Breast Cancer concludes that "studies confirm previous observations that there appears to be an association between alcohol intake and increased risk of breast cancer in women. On balance, there was a weak association between the amount of alcohol consumed and the relative risk."[17]

The National Institute on Alcohol Abuse and Alcoholism (NIAAA) concludes that "Chronic alcohol consumption has been associated with a small (averaging 10 percent) increase in a woman's risk of breast cancer."[18][19][20][21] According to these studies, the risk appears to increase as the quantity and duration of alcohol consumption increases. Other studies, however, have found no evidence of such a link.[22][23][24]

The Committee on Carcinogenicity of Chemicals in Food, Consumer Products Non-Technical Summary concludes, "the new research estimates that a woman drinking an average of two units of alcohol per day has a lifetime risk of developing breast cancer 8% higher than a woman who drinks an average of one unit of alcohol per day.[25] The risk of breast cancer further increases with each additional drink consumed per day. The research also concludes that approximately 6% (between 3.2% and 8.8%) of breast cancers reported in the UK each year could be prevented if drinking was reduced to a very low level (i.e. less than 1 unit/week)." A review article from JAMA also found that breast cancer incidence seems to increase with increasing alcohol consumption.[26] It has been reported that "two drinks daily increase the risk of getting breast cancer by about 25 percent" (NCI), but the evidence is inconsistent. The Framingham study has carefully tracked individuals since the 1940s. Data from that research found that drinking alcohol moderately did not increase breast cancer risk (Wellness Facts). Similarly, research by the Danish National Institute for Public Health found that moderate drinking had virtually no effect on breast cancer risk.[27]

One study suggests that women who frequently drink red wine may have an increased risk of developing breast cancer.[28]

"Folate intake counteracts breast cancer risk associated with alcohol consumption"[29] and "women who drink alcohol and have a high folate intake are not at increased risk of cancer."[30] Those who have a high (200 micrograms or more per day) level of folate (folic acid or Vitamin B9) in their diet are not at increased risk of breast cancer compared to those who abstain from alcohol.[31] Foods rich in folate include citrus fruits, citrus juices, dark green leafy vegetables (such as spinach), dried beans, and peas. Vitamin B9 can also be taken in a multivitamin pill.

Obesity

Gaining weight after menopause can increase a woman's risk. A recent study found that putting on 9.9kg (22lbs) after menopause increased the risk of developing breast cancer by 18%.[32]

Hormones

Persistently increased blood levels of estrogen are associated with an increased risk of breast cancer, as are increased levels of the androgens androstenedione and testosterone (which can be directly converted by aromatase to the estrogens estrone and estradiol, respectively). Increased blood levels of progesterone are associated with a decreased risk of breast cancer in premenopausal women.[33] A number of circumstances which increase exposure to endogenous estrogens including not having children, delaying first childbirth, not breastfeeding, early menarche (the first menstrual period) and late menopause are suspected of increasing lifetime risk for developing breast cancer.[34]

Hormonal contraceptives may produce a slight increase in the risk of breast cancer diagnosis among current and recent users, but this appears to be a short-term effect. In 1996 the largest collaborative reanalysis of individual data on over 150,000 women in 54 studies of breast cancer found a relative risk (RR) of 1.24 of breast cancer diagnosis among current combined oral contraceptive pill users; 10 or more years after stopping, no difference was seen. Further, the cancers diagnosed in women who had ever used hormonal contraceptives were less advanced than those in nonusers, raising the possibility that the small excess among users was due to increased detection.[35][36] The relative risk of breast cancer diagnosis associated with current and recent use of hormonal contraceptives did not appear to vary with family history of breast cancer.[37]

Data exist from both observational and randomized clinical trials regarding the association between postmenopausal hormone replacement therapy (HRT) and breast cancer. The largest meta-analysis (1997) of data from 51 observational studies, indicated a relative risk of breast cancer of 1.35 for women who had used HRT for 5 or more years after menopause. The estrogen-plus-progestin arm of the Women's Health Initiative (WHI), a randomized controlled trial, which randomized more than 16,000 postmenopausal women to receive combined hormone therapy or placebo, was halted early (2002) because health risks exceeded benefits. One of the adverse outcomes prompting closure was a significant increase in both total and invasive breast cancers (RR = 1.24) in women randomized to receive estrogen and progestin for an average of 5 years. HRT-related breast cancers had adverse prognostic characteristics (more advanced stages and larger tumors) compared with cancers occurring in the placebo group, and HRT was also associated with a substantial increase in abnormal mammograms. Short-term use of hormones for treatment of menopausal symptoms appears to confer little or no breast cancer risk.[37]

Environmental risk factors

Tobacco

Most studies have not found an increased risk of breast cancer from active tobacco smoking, although a number of studies suggest an increased risk of breast cancer in both active smokers and those exposed to secondhand smoke compared to women who reported no exposure to secondhand smoke.[7]

Radiation

Women who have received high-dose ionizing radiation to the chest (for example, as treatments for other cancers) have a relative risk of breast cancer between 2.1 to 4.0.[7]

Impact of environmental estrogenic mimics

Although environmental exposures are not generally cited as risk factors for the disease (except for diet, pharmaceuticals and radiation), a substantial and growing body of evidence indicates that exposures to certain toxic chemicals and hormone-mimicking compounds including chemicals used in pesticides, cosmetics and cleaning products contribute to the development of breast cancer. A recent Canadian study concluded that female farm workers are three times more likely to have breast cancer.[38] The increasing prevalence of these substances in the environment may explain the increasing incidence of breast cancer, though direct evidence is sparse.

Dioxins

Although not well-quantified, there has long been a concern about risk associated with environmental estrogenic compounds, such as dioxins.[citation needed]

Light levels

Researchers at the National Cancer Institute and National Institute of Environmental Health Sciences have concluded a study that suggests that artificial light during the night can be a factor for breast cancer.[39]

Viral breast cancer pathogenesis research

Humans are not the only mammals susceptible to breast cancer. Some strains of mice, namely the house mouse (Mus domesticus) are prone to breast cancer which is caused by infection with the mouse mammary tumour virus (MMTV or "Bittner virus" for its discoverer Hans Bittner), by random insertional mutagenesis. This finding is taken to mean that a viral etiology of human breast cancer is at least possible, though there is no definitive evidence to support the claim that MMTV causes human breast cancer. For example, there may be critical differences between cancer pathogenesis in mice and people. The understanding of the role of MMTV or other viruses in human breast cancer is preliminary as of May 2007.

Factors with minimal or no impact on breast cancer risk

Abortion

Studies in rats[40] led to speculation that abortion may increase the risk of breast cancer because of hormones initiating breast tissue growth in early pregnancy. Some early interview[41] and record[42] based case-control studies indicated a possible correlation, but more recent record based studies[43][44][45] and a large meta-analysis[46] study do not support this association. The subject was examined by a National Cancer Institute (NCI) workshop in 2003, in response to the Bush Administration's alteration of the NCI's website to emphasize studies indicating a potential link.[47] The NCI expert panel concluded, with the strongest level of evidence, that induced abortion is not associated with an increased breast cancer risk.[48]

Deodorants

Much has been made of the possible contribution of aluminum-containing underarm antiperspirants to the incidence of breast cancer, since the most common location of a breast cancer is the upper outer quadrant of the breast. Aluminum salts, such as those used in anti-perspirants, have recently been classified as metalloestrogens. In research published in the Journal of Applied Toxicology, Dr. Philippa D. Darbre of the University of Reading has shown that aluminum salts increase estrogen-related gene expression in human breast cancer cells grown in the laboratory.[49][50][51] Fortunately, this in-vitro association between aluminum salts and estrogen activity does not translate into an increased risk of breast cancer in humans. The lack of association between underarm deodorants and breast cancer has been the subject of a number of research articles.[52][53]

Fertility treatments

There is no persuasive connection between fertility medications and breast cancer.[54]

References

  1. ↑ 1.0 1.1 Giordano, Sharon H (May 2004). "Breast carcinoma in men". Cancer. American Cancer Society. 101 (1): 51–57. Unknown parameter |coauthors= ignored (help)
  2. ↑ "Individual Risk Factors". BreastCancer.org. Retrieved 2007-03-11.
  3. ↑ Yager JD (2006). "Estrogen carcinogenesis in breast cancer". New Engl J Med. 354 (3): 270–82. PMID 16421368. Unknown parameter |coauthors= ignored (help)
  4. ↑ Chlebowski RT, Blackburn GL, Thomson CA, Nixon DW, Shapiro A, Hoy MK; et al. "Dietary fat reduction and breast cancer outcome: interim efficacy results from the Women's Intervention Nutrition Study (WINS)". J Natl Cancer Inst. 98 (24): 1767–1776. PMID 17179478.
  5. ↑ 5.0 5.1 Boffetta, Paolo (2006-03-23). "The burden of cancer attributable to alcohol drinking". International Journal of Cancer. Wiley-Liss, Inc. 119 (4): 884–887. doi:10.1002/ijc.21903. PMID 16557583. Retrieved 2006-10-09. Unknown parameter |coauthors= ignored (help)
  6. ↑ BBC report Weight link to breast cancer risk
  7. ↑ 7.0 7.1 7.2 ACS (2005). "Breast Cancer Facts & Figures 2005-2006" (PDF). Retrieved 2007-04-26.
  8. ↑ "Individual Risk Factors". BreastCander.org. Retrieved 2007-03-11.
  9. ↑ 9.0 9.1 Malone KE, Daling JR, Thompson JD, O'Brien CA, Francisco LV, Ostrander EA (1998). "BRCA1 mutations and breast cancer in the general population: analyses in women before age 35 years and in women before age 45 years with first-degree family history". JAMA. 279 (12): 922–9. PMID 9544766.
  10. ↑ Emilie Auriol, Lise-Marie Billard, Frederique Magdinier, Robert Dante (2005). "Specific binding of the methyl binding domain protein 2 at the BRCA1-NBR2 locus". Nucleic Acids Research. 33 (13): 4243–4254.
  11. ↑ Chlebowski RT, Blackburn GL, Thomson CA, Nixon DW, Shapiro A, Hoy MK; et al. "Dietary fat reduction and breast cancer outcome: interim efficacy results from the Women's Intervention Nutrition Study (WINS)". J Natl Cancer Inst. 98 (24): 1767–1776. PMID 17179478.
  12. ↑ Hunter DJ, Spiegelman D, Adami HO; et al. (1996). "Cohort studies of fat intake and the risk of breast cancer--a pooled analysis". N. Engl. J. Med. 334 (6): 356–61. PMID 8538706.
  13. ↑ Prentice RL, Caan B, Chlebowski RT; et al. (2006). "Low-fat dietary pattern and risk of invasive breast cancer: the Women's Health Initiative Randomized Controlled Dietary Modification Trial". JAMA. 295 (6): 629–42. doi:10.1001/jama.295.6.629. PMID 16467232.
  14. ↑ Terry P, Wolk A, Persson I, Magnusson C title = Brassica Vegetables and Breast Cancer Risk (2001). JAMA. 285 (23): 2975–2976. Missing or empty |title= (help)
  15. ↑ Nelson N title = Migrant Studies Aid Search for Factors Linked to Breast Cancer Risk (2006). JAMA. 8 (7): 436–438. Missing or empty |title= (help)
  16. ↑ "Statistics for 2007". American Cancer Society. Retrieved 2007-03-11.
  17. ↑ "Review of Alcohol: Association with Breast Cancer" (PDF). U.K. Dept. of Health. Retrieved 2007-03-11.
  18. ↑ Friedenreich C, Howe G, Miller A, Jain M (1993). "A cohort study of alcohol consumption and risk of breast cancer". Am J Epidemiol. 137 (5): 512–20. PMID 8465803.
  19. ↑ Longnecker M, Berlin J, Orza M, Chalmers T (1988). "A meta-analysis of alcohol consumption in relation to risk of breast cancer". JAMA. 260 (5): 652–6. PMID 3392790.
  20. ↑ Longnecker MP (1992). "Alcohol consumption in relation to risk of cancers of the breast and large bowel". Alcohol Health & Research World. 16 (3): 223–229.
  21. ↑ Nasca P, Baptiste M, Field N, Metzger B, Black M, Kwon C, Jacobson H (1990). "An epidemiological case-control study of breast cancer and alcohol consumption". Int J Epidemiol. 19 (3): 532–8. PMID 2262245.
  22. ↑ Chu S, Lee N, Wingo P, Webster L (1989). "Alcohol consumption and the risk of breast cancer". Am J Epidemiol. 130 (5): 867–77. PMID 2683749.
  23. ↑ Schatzkin A, Piantadosi S, Miccozzi M, Bartee D (1989). "Alcohol consumption and breast cancer: a cross-national correlation study". Int J Epidemiol. 18 (1): 28–31. PMID 2722377.
  24. ↑ Webster L, Layde P, Wingo P, Ory H (1983). "Alcohol consumption and risk of breast cancer". Lancet. 2 (8352): 724–6. PMID 6136850.
  25. ↑ "CONSUMPTION OF ALCOHOLIC BEVERAGES AND RISK OF BREAST CANCER IN WOMEN" (PDF). U.K. Dept. of Health. Retrieved 2007-03-11.
  26. ↑ Singletary KW, Gapstur SM (2001). "Alcohol and breast cancer: review of epidemiologic and experimental evidence and potential mechanisms". JAMA. 286 (17): 2143–51. PMID 11694156.
  27. ↑ Petri A, Tjønneland A, Gamborg M, Johansen D, Høidrup S, Sørensen T, Grønbaek M (2004). "Alcohol intake, type of beverage, and risk of breast cancer in pre- and postmenopausal women". Alcohol Clin Exp Res. 28 (7): 1084–90. PMID 15252295.
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  29. ↑ Mayo Clinic news release June 26 2001 "Folate Intake Counteracts Breast Cancer Risk Associated with Alcohol Consumption"
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  36. ↑ Collaborative Group on Hormonal Factors in Breast Cancer (1996). "Breast cancer and hormonal contraceptives: further results". Contraception. 54 (3 Suppl): 1S–106S. PMID 8899264.
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  38. ↑ Ctv.Ca News Staff (2006-10-12). "Breast cancer more likely in farm workers: study". Ctv.Ca. Retrieved 2007-03-11.
  39. ↑ The Independent Avoid breast cancer. Sleep in the dark...
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  43. ↑ Melbye M, Wohlfahrt J, Olsen J, Frisch M, Westergaard T, Helweg-Larsen K, Andersen P (1997). "Induced abortion and the risk of breast cancer". N Engl J Med. 336 (2): 81–5. PMID 8988884.
  44. ↑ Reeves G, Kan S, Key T, Tjønneland A, Olsen A, Overvad K, Peeters P, Clavel-Chapelon F, Paoletti X, Berrino F, Krogh V, Palli D, Tumino R, Panico S, Vineis P, Gonzalez C, Ardanaz E, Martinez C, Amiano P, Quiros J, Tormo M, Khaw K, Trichopoulou A, Psaltopoulou T, Kalapothaki V, Nagel G, Chang-Claude J, Boeing H, Lahmann P, Wirfält E, Kaaks R, Riboli E (2006). "Breast cancer risk in relation to abortion: Results from the EPIC study". Int. J. Cancer. 119 (7): 1741–5. PMID 16646050.
  45. ↑ Karin B. Michels, ScD, PhD; Fei Xue, MD; Graham A. Colditz, MD, DrPH; Walter C. Willett, MD, DrPH. "Induced and Spontaneous Abortion and Incidence of Breast Cancer Among Young Women." Arch Intern Med. 2007;167:814-820. Abstract.
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  51. ↑ Darbre, PD (2005). "Aluminium, antiperspirants and breast cancer". Journal of Inorganic Biochemistry. Elsevier. 99 (9): 1912–9. PMID 16045991mmmmmmiii Check |pmid= value (help).
  52. ↑ Surendran A (2004). "Studies linking breast cancer to deodorants smell rotten, experts say". Nat. Med. 10 (3): 216. doi:10.1038/nm0304-216b. PMID 14991030.
  53. ↑ "Antiperspirants don't cause breast cancer". Harvard women's health watch. 10 (5): 7. 2003. PMID 12543590.
  54. ↑ Potashnik G, Lerner-Geva L, Genkin L, Chetrit A, Lunenfeld E, Porath A (1999). "Fertility drugs and the risk of breast and ovarian cancers: results of a long-term follow-up study". Fertil. Steril. 71 (5): 853–9. PMID 10231045.

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