Breast cancer mammography
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1], Assistant Editor(s)-In-Chief: Soroush Seifirad, M.D.[2]Jack Khouri; Ammu Susheela, M.D. [3]
Overview
Mammography is the process of using low-dose X-rays (usually around 0.7 mSv) to examine the human breast. It is used to look for different types of tumors and cysts. Mammography has been proven to reduce mortality from breast cancer. No other imaging technique has been shown to reduce risk, but self-breast examination (SBE) and physician examination are essential parts of regular breast care. In some countries routine (annual to five-yearly) mammography of older women is encouraged as a screening method to diagnose early breast cancer. Screening mammograms were first proven to save lives in research published by Sam Shapiro, Philip Strax and Louis Venet in 1966.
Like all x-rays, mammograms use doses of ionizing radiation to create this image. Radiologists then analyze the image for any abnormal growths. It is normal to use longer wavelength X-rays (typically Mo-K) than those used for radiography of bones.
At this time, mammography along with physical breast examination is still the modality of choice for screening for early breast cancer. It is the gold-standard which other imaging tests are compared with. CT has no real role in diagnosing breast cancer at the present. Ultrasound, Ductography, and Magnetic Resonance are adjuncts to mammography. Ultrasound is typically used for further evaluation of masses found on mammography or palpable masses not seen on mammograms. Ductograms are useful for evaluation of bloody nipple discharge when the mammogram is non-diagnostic. MRI can be useful for further evaluation of questionable findings, or sometimes for pre-surgical evaluation to look for additional lesions. Stereotactic breast biopsies are another common method for further evaluation of suspicious findings.
Mammography has a false-negative (missed cancer) rate of at least 10 percent. This is partly due to dense tissues obscuring the cancer and the fact that the appearance of cancer on mammograms has a large overlap with the appearance of normal tissues.
Mammography may be performed to detect breast cancer.
Advantages
- Mammography has been estimated to reduce breast cancer-related mortality by 20-30%.[1]
Disadvantages
- Evidence in favor of mammography screening comes from eight randomized controlled clinical trials from the 1960s through 1980s.
- Many of these trials have been criticized for methodological errors, and the results were summarized in a review article published in 1993.[2]
- False positive reports are a major problem of mammography breast cancer screening. Approximately 7% of all mammography screenings are false positives. [3]
- Data reported in the UK Million Woman Study indicates that if 134 mammograms are performed, 20 women will be called back for suspicious findings, and four biopsies will be necessary, to diagnose one cancer. Recall rates are higher in the U.S. than in the UK.[4]
- Mammography in women under 50 years of age can be imprecise due to breast density.
- Breast density is an independent adverse prognostic factor on breast cancer prognosis. [5]
- It could delay diagnosis of breast cancer using mammography, additionally having dense breast is a risk factor for developing breast cancer.
Procedure
- During the procedure, the breast is compressed by a dedicated mammography machine to even out the tissue, to increase image quality, and to hold the breast still (preventing motion blur). Both front and side images of the breast are taken. Deodorant, talcum powder or lotion may show up on the X-ray as calcium spots, and women are discouraged from applying these on the day of their investigation. Until some years ago, mammography was typically performed with screen-film cassettes. Now, mammography is undergoing transition to digital detectors, known as Full Field Digital Mammography (FFDM). This progress is some years later than in general radiology. This is due to several factors:
- the higher resolution demands in mammography,
- significantly increased expense of the equipment,
- the fact that digital mammography has never been shown to be superior to film-screen mammography for the diagnosis of breast cancer. Computed radiography (CR) may help speed the transition. CR allows facilities to continue to use their existing screen-film units but replace the cassettes with an imaging plate that acts as a digital adapter. As of March 1, 2007, 18.3% of facilities in the United States and its territories have at least one FFDM unit. (The FDA includes computed radiography units in this figure.)
- After a screening mammogram, some women may have areas of concern which can't be resolved with only the information available from the screening mammogram. They would then be called back for a "diagnostic mammogram". This phrase is essentially a problem-solving mammogram. During this session, the radiologist will be monitoring each of the additional films as they are taken to determine the cause of the abnormal appearance.
- During the procedure, the breast is compressed by a dedicated mammography machine to:
- Even out the tissue
- Increase image quality
- Hold the breast still (preventing motion blur).
- Due to imaging limitations, some elements may show up on x-ray as calcium spots. For this reason, women are discouraged from applying the following on the day of the mammogram.
- The outcome of a mammogram may be benign or may require further investigation. If the cause cannot be determined to be benign with sufficient certainty, a biopsy will be recommended.
- The biopsy procedure will be used to obtain actual tissue from the site for the pathologist to examine microscopically to determine the precise cause of the abnormality.
- In the past, biopsies were most frequently done in surgery, under local or general anesthesia. T
- he majority are now done with needles using either ultrasound or mammographic guidance to be sure that the area of concern is the area that is biopsied.
- One study shows that needle biopsies of liver malignancies rarely increase the likelihood that cancer will spread, and has not been found to occur with breast needle biopsies.
BI-RADS
There is a standard system for reporting the results of a mammogram, which is called the Breast Imaging-Reporting and Data System, or BI-RADS.
| Category | Meaning |
| 0 | An unclear result with a need for more tests or comparison with previous mammograms |
| 1 | No abnormalities |
| 2 | No sign of cancer but some abnormalities present, such as benign calcifications |
| 3 | Some abnormalities that are very likely to be benign but need following up |
| 4 | Abnormalities that could be cancerous, possibly requiring a biopsy |
| 5 | Abnormalities very likely to be cancerous, requiring a biopsy |
| 6 | Cancer is present, requiring mammograms to check progress |
Screening guidelines
- In 2009, the U.S. Preventive Services Task Force (USPSTF) revised their 2002 guideline wherein a mammogram was recommended every 1-2 years for women of 40 years and over.
- One of the reasons for this change *A number of studies demonstrated an increased risk of false-positive results when screening starts at a younger age or takes place every year.
- Currently, USPSTF recommends screening mammography for women aged 50 to 74 years, every 2 years.
- Although this advice is in line with that offered in many European countries, it differs with the recommendations of some other U.S. organizations.
- The American College of Radiology and the Society of Breast Imaging both continue to recommend annual mammograms for women starting at age 40.
- The current guidelines issued by the American Cancer Society advise a mammogram every year for women of 45 to 54 years, and every 2 years for women of 55 years and older.
- In light of the debate, various emerging technologies are now being suggested as alternative options for breast cancer screening.
Mammography risks
- There are some potential risks that are considered to be associated with mammography and mammograms. They include the following:
- They require repeated exposure to radiation, which may cause a very small risk of cancer if used over a lifetime.
- They can lead to non-invasive cancers being diagnosed and treated when treatment is not necessarily required.
- They are not as effective for women with dense breast tissue or breast implants.
- They can lead to women choosing double mastectomies as a preventive measure.
- They have a high rate of false-positive results, which can result in unnecessary biopsies and additional screening. False-positive results are those that suggest that cancer is present when it is not.
- 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 (OR between 1.3 and 2 with respect to the patients' risk and exposure) observed compared to that of high-risk women not exposed to low-dose radiation.
- Pooled OR revealed an increased risk of breast cancer among high-risk women due to low-dose radiation exposure (OR = 1.3, 95% CI: 0.9- 1.8).
- Exposure before age 20 (OR = 2.0, 95% CI: 1.3-3.1)
- A mean of ≥5 exposures (OR = 1.8, 95% CI: 1.1-3.0)
- When using low-dose radiation among high-risk women, a careful approach is needed, by means of
- They recommended a careful approach in these subgroup of patients as follows:
- Reducing repeated exposure,
- Avoidance of exposure at a younger age
- Using non-ionising screening techniques.
- 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".
Modern Mammography utilities
3D-Tomosynthesis
- While traditional mammograms are 2-D and provide a flat image, tomosynthesis creates a 3-D image.
- Standard mammograms and tomosynthesis both use X-rays.
- This screening procedure is similar to a mammogram, but it produces a 3-D image rather than a flat one.
- As a result, it may provide more accurate information about whether or not there are any changes in the breast.
Alternatives to mammography[edit | edit source]
While the cost of mammography is relatively low, its sensitivity is not ideal, with reports listing the range from 45% to about 90% depending on factors such as the density of the breast. Neither is the X-ray based technology completely benign, as noted above. Therefore there is considerable ongoing research into the use of alternative technologies.
One approach, contrast enhanced magnetic resonance imaging (MRI), has shown substantial progress. In this method, the breast is scanned in an MRI device before and after the intravascular injection of a contrast agent (Gadolinium DTPA). The pre-contrast images are "subtracted" from the post-contrast images, and any areas that have increased blood flow are seen as bright spots on a dark background. Since breast cancers generally have an increased blood supply, the contrast agent causes these lesions to "light up" on the images. The available literature suggests that the sensitivity of contrast-enhanced breast MRI is considerably higher than that of either radiographic mammography or ultrasound and is generally reported to be in excess of 95% (though not all reported studies have been as encouraging). The specificity (the confidence that a lesion is cancerous and not a false positive) is only fair, thus a positive finding by MRI should not be interpreted as a definitive diagnosis. The reports of 4,271 breast MRIs from eight large scale clinical trials were reviewed recently by CD Lehman. Overall the sensitivity ranged from 71% to 100% in these reports, however the call-back rates were low at 10% and the risk of having a benign biopsy was reported at 5%, a significant improvement over mammography.
Several medical instrument vendors have entered this arena with breast MRI solutions. One company, Aurora Systems, stands out as being the only manufacturer to make a breast-dedicated unit and as the exclusive patent holder of certain solutions to fat signal suppression that appear to be more or less essential. Siemens, General Electric and Philips Medical, the leading manufacturers of MRI instruments, offer breast MRI products or add-ons, and several third-party companies (e.g., MRI Devices/IGC) offer aftermarket products to enable breast MRI on conventional MRI instruments.
Regulation[edit | edit source]
Mammography facilities in the United States and its territories (including military bases) are subject to the Mammography Quality Standards Act (MQSA). The act requires annual inspections and accredition every 3 years through an FDA-approved body. Facilities found deficient during the inspection or accreditation process can be barred from performing mammograms until corrective action has been verified or, in extreme cases, can be required to notify past patients that their exams were sub-standard and should not be trusted.
Despite passage of the MQSA by congress in 1992 and the nearly 1 billion dollar cost, the aggregate sensitivity of mammography in the USA is similar to what it was in the 1970s.
At this time MQSA applies only to traditional mammography and not related scans such as breast ultrasound, stereotactic breast biospy, or breast MRI.
References
- ↑ Elwood J, Cox B, Richardson A. "The effectiveness of breast cancer screening by mammography in younger women". Online J Curr Clin Trials. Doc No 32: [23, 227 words, 195 paragraphs]. PMID 8305999.
- ↑ Fletcher SW, Black W, Harris R, Rimer BK, Shapiro S (1993). "Report of the International Workshop on Screening for Breast Cancer". J. Natl. Cancer Inst. 85 (20): 1644–56. PMID 8105098.
|access-date=requires|url=(help) - ↑ Brewer NT, Salz T, Lillie SE (2007). "Systematic review: the long-term effects of false-positive mammograms". Ann Intern Med. 146 (7): 502–10. PMID 17404352.
- ↑ Smith-Bindman R, Ballard-Barbash R, Miglioretti DL, Patnick J, Kerlikowske K (2005). "Comparing the performance of mammography screening in the USA and the UK". Journal of medical screening. 12 (1): 50–4. doi:10.1258/0969141053279130. PMID 15814020.
- ↑ Armstrong K, Moye E, Williams S, Berlin JA, Reynolds EE (2007). "Screening mammography in women 40 to 49 years of age: a systematic review for the American College of Physicians". Ann. Intern. Med. 146 (7): 516–26. PMID 17404354.