View source for Breast cancer risk factors

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{{CMG}}{{AE}} {{Soroush}}{{MGS}}
{{Breast cancer}}
==Overview==
Common risk factors in the development of breast cancer are family history, dense breast, obesity, radiation therapy, older age at first birth or never having given birth, hormone replacement therapy, and alcohol.
==Common Risk Factor==
* Although less than 15 percent of women with breast cancer have a positive family history, a woman’s risk of breast cancer nearly doubles if she has a first-degree relative (mother, sister, daughter)  with the history of breast cancer.
* Around 5-10 percent of breast cancers are due to inherited gene mutations either from one’s mother or father. 
* ''BRCA1'' and ''BRCA2 mutations'' are the most common genetic abnormality in breast cancer.<ref name="pmid15546503">Yoshida K, Miki Y (2004) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=15546503 Role of BRCA1 and BRCA2 as regulators of DNA repair, transcription, and cell cycle in response to DNA damage.] ''Cancer Sci'' 95 (11):866-71. PMID: [https://pubmed.gov/15546503 15546503]</ref> 
:* Women with a ''BRCA1 and''  ''BRCA2'' mutation have up to a 72% and 69% lifetime risk of developing breast cancer respectively.
:* Patients with ''BRCA1'' or ''BRCA2''  are often younger compared to their counterparts without these mutations. 
:* There is also an increased risk of developing ovarian cancer risk in subjects with mutated BRCA1 and 2.
:* Although ''BRCA1'' mutations are barely correlated to breast cancer in men, a 6.8% increased risk of developing breast cancer has been observed in men with ''BRCA2'' mutations.
* We should keep in mind that around 85% of women with breast cancers have no family history.

'''A personal history of breast cancer or benign (noncancer) breast disease'''<ref name="CRF">Breast Cancer. National Cancer Institute (2016) http://www.cancer.gov/types/breast/patient/breast-prevention-pdq#section/_12 Accessed on January 15, 2016 </ref>
*Women with any of the following have an increased risk of breast cancer:
:*A personal history of invasive breast cancer, ductal carcinoma in situ (DCIS), or lobular carcinoma in situ (LCIS).
:*A personal history of benign (noncancer) breast disease.
'''A family history of breast cancer'''
*Women with a family history of breast cancer in a first-degree relative (mother, sister, or daughter) have an increased risk of breast cancer.<ref name="pmid28578505">Brewer HR, Jones ME, Schoemaker MJ, Ashworth A, Swerdlow AJ (2017) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=28578505 Family history and risk of breast cancer: an analysis accounting for family structure.] ''Breast Cancer Res Treat'' 165 (1):193-200. [http://dx.doi.org/10.1007/s10549-017-4325-2 DOI:10.1007/s10549-017-4325-2] PMID: [https://pubmed.gov/28578505 28578505]</ref>
'''Inherited gene changes'''
*Women who have inherited changes in the BRCA1 and BRCA2 genes or in certain other genes have a higher risk of breast cancer, ovarian cancer, and maybe colon cancer. 
:*The risk of breast cancer caused by inherited gene changes depends on the type of gene mutation, family history of cancer, and other factors.
*Men who have inherited certain changes in the BRCA2 gene have a higher risk of breast, prostate, and pancreatic cancers, and lymphoma.
'''Dense breasts'''
*Having breast tissue that is dense on a mammogram is a factor in breast cancer risk.<ref name="pmid25763718">Freer PE (2015) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=25763718 Mammographic breast density: impact on breast cancer risk and implications for screening.] ''Radiographics'' 35 (2):302-15. [http://dx.doi.org/10.1148/rg.352140106 DOI:10.1148/rg.352140106] PMID: [https://pubmed.gov/25763718 25763718]</ref> 
:*The level of risk depends on how dense the breast tissue is. 
:*Women with very dense breasts have a higher risk of breast cancer than women with low breast density.
:*Increased breast density is often an inherited trait, but it may also occur in women who:
::*Have not had children
::*Have the first pregnancy late in life
::*Take postmenopausal hormones (HRT) 
::*Drink alcohol
'''Exposure of breast tissue to estrogen made in the body'''
*Estrogen is a hormone made by the body. It helps the body develop and maintain female sex characteristics. Being exposed to estrogen over a long time may increase the risk of breast cancer. Estrogen levels are highest during the years a woman is menstruating.<ref name="pmid20104523">Yue W, Wang JP, Li Y, Fan P, Liu G, Zhang N et al. (2010) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=20104523 Effects of estrogen on breast cancer development: Role of estrogen receptor independent mechanisms.] ''Int J Cancer'' 127 (8):1748-57. [http://dx.doi.org/10.1002/ijc.25207 DOI:10.1002/ijc.25207] PMID: [https://pubmed.gov/20104523 20104523]</ref>
*A woman's exposure to estrogen is increased in the following ways:
:*Early menstruation: Beginning to have menstrual periods at age 11 or younger increases the number of years the breast tissue is exposed to estrogen.
:*Starting menopause at a later age: The more years a woman menstruates, the longer her breast tissue is exposed to estrogen.
:*Older age at first birth or never having given birth: Because estrogen levels are lower during pregnancy, breast tissue is exposed to more estrogen in women who become pregnant for the first time after age 35 or who never become pregnant.
'''Taking hormone therapy for symptoms of menopause'''
*Hormones, such as estrogen and progesterone, can be made into a pill form in a laboratory. Estrogen, progestin, or both may be given to replace the estrogen no longer made by the ovaries in postmenopausal women or women who have had their ovaries removed. This is called hormone replacement therapy (HRT) or hormone therapy (HT). Combination HRT/HT is estrogen combined with progestin. This type of HRT/HT increases the risk of breast cancer. Studies show that when women stop taking estrogen combined with progestin, the risk of breast cancer decreases.<ref name="pmid21253794">Howell A, Evans GD (2011) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=21253794 Hormone replacement therapy and breast cancer.] ''Recent Results Cancer Res'' 188 ():115-24. [http://dx.doi.org/10.1007/978-3-642-10858-7_10 DOI:10.1007/978-3-642-10858-7_10] PMID: [https://pubmed.gov/21253794 21253794]</ref> 
'''Radiation therapy to the breast or chest'''
*Radiation therapy to the chest for the treatment of cancer increases the risk of breast cancer, starting 10 years after treatment. The risk of breast cancer depends on the dose of radiation and the age at which it is given.<ref name="pmid19930978">Ng AK, Travis LB (2009) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=19930978 Radiation therapy and breast cancer risk.] ''J Natl Compr Canc Netw'' 7 (10):1121-8. PMID: [https://pubmed.gov/19930978 19930978]</ref> The risk is highest if radiation treatment was used during puberty when breasts are forming.
*Radiation therapy to treat cancer in one breast does not appear to increase the risk of cancer in the other breast.
*For women who have inherited changes in the BRCA1 and BRCA2 genes, exposure to radiation, such as that from chest x-rays, may further increase the risk of breast cancer, especially in women who were x-rayed before 20 years of age.
'''Obesity'''
*Obesity increases the risk of breast cancer, especially in postmenopausal women who have not used hormone replacement therapy.<ref name="pmid28763097">Picon-Ruiz M, Morata-Tarifa C, Valle-Goffin JJ, Friedman ER, Slingerland JM (2017) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=28763097 Obesity and adverse breast cancer risk and outcome: Mechanistic insights and strategies for intervention.] ''CA Cancer J Clin'' 67 (5):378-397. [http://dx.doi.org/10.3322/caac.21405 DOI:10.3322/caac.21405] PMID: [https://pubmed.gov/28763097 28763097]</ref>
'''Drinking alcohol'''
*Drinking alcohol increases the risk of breast cancer. The level of risk rises as the amount of alcohol consumed rises.<ref name="pmid24265860">McDonald JA, Goyal A, Terry MB (2013) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=24265860 Alcohol Intake and Breast Cancer Risk: Weighing the Overall Evidence.] ''Curr Breast Cancer Rep'' 5 (3):. [http://dx.doi.org/10.1007/s12609-013-0114-z DOI:10.1007/s12609-013-0114-z] PMID: [https://pubmed.gov/24265860 24265860]</ref>
==Less Common 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 [[passive smoking|secondhand smoke]] compared to women who reported no exposure to secondhand smoke.<ref name="acs bc facts 2005-6" />

====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.<!--
  --><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>
*Serial mammography might slightly increase the risk of developing breast cancer in high-risk patients such as patients with a family history of breast cancer and patients with known genetic carcinogenic mutations.
:*According to a recently published study by Jansen-van der Weide et.al. average increased the risk of breast cancer because of low-dose radiation exposure was 1.5 times higher than that of high-risk women not exposed to low-dose radiation.
:*High-risk women exposed before age 20 or with five or more exposures were 2.5 times more likely to develop breast cancer compared to the high-risk women whom were not exposed to low-dose radiation. 
:*They recommend careful approach in these subgroup of patients, and if possible other diagnostic approaches are better options for these subjects.
:*According to another study by Diana L. Miglioretti et.al. radiation-induced breast cancer incidence and mortality from digital mammography screening are impacted by:
:*Dose variability from screening and resultant diagnostic work-up,
::*Initiation age
::*Screening frequency. 
::*Women with large breasts may be at higher risk of radiation-induced breast cancer;
*'''However, we should keep in mind that "the benefits of screening outweigh these risks".'''

====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.<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 rising incidence of breast cancer, though direct evidence is sparse.

====Dioxins====
*Although not well-quantified, there has long been a concern about the risk associated with environmental estrogenic compounds, such as [[dioxins]]. <ref name="pmid25849111">Danjou AM, Fervers B, Boutron-Ruault MC, Philip T, Clavel-Chapelon F, Dossus L (2015) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=25849111 Estimated dietary dioxin exposure and breast cancer risk among women from the French E3N prospective cohort.] ''Breast Cancer Res'' 17 ():39. [http://dx.doi.org/10.1186/s13058-015-0536-9 DOI:10.1186/s13058-015-0536-9] PMID: [https://pubmed.gov/25849111 25849111]</ref><ref name="pmid12117637">Warner M, Eskenazi B, Mocarelli P, Gerthoux PM, Samuels S, Needham L et al. (2002) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=12117637 Serum dioxin concentrations and breast cancer risk in the Seveso Women's Health Study.] ''Environ Health Perspect'' 110 (7):625-8. [http://dx.doi.org/10.1289/ehp.02110625 DOI:10.1289/ehp.02110625] PMID: [https://pubmed.gov/12117637 12117637]</ref>

====Light levels====
*Researchers at the [[National Cancer Institute]] and [[National Institute of Environmental Health Sciences]] have conducted 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>
==References==
{{Reflist|2}}

[[Category:Disease]]
[[Category:Types of cancer]]
[[Category:Breast]]
[[Category:Hereditary cancers]]
[[Category:Mature chapter]]
[[Category:Oncology]]

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