Mammography

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Mammography is the process of using low-dose X-rays (usually around 0.7 mSv) to examine the human breast. It’s 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 an 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 test of choice for screening for early breast cancer. It’s the gold-standard which other imaging tests are compared with. CT (cat scan) has no real role in diagnosing breast cancer at the present. Ultrasound, Ductography, and Magnetic Resonance (MRI) can be used to augment mammography. Ultrasound is typically used for further evaluation of masses found on mammography or felt masses not seen on mammograms. Ductograms are useful for evaluation of bloody nipple discharge when the mammogram shows nothing wrong. 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.


Contents

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 asked not to apply these on the day of their test.

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). The progress of this transition is somewhat slower than in general radiology. This is due to several factors:

  • The higher resolution demands in mammography, pictures need to be sharper to be useful,
  • The equipment is significantly more expensive,
  • 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.)

"Work-up" process

In the past several years, the "work-up" process has become quite formalized. It generally consists of screening mammography, diagnostic mammography, and biopsy when necessary. 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 essentially means 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. Ultrasound is often used at this point, as well.

Generally the cause of the unusual appearance is found to be benign. 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. The 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.[1]

Results

Often women are quite distressed to be called back for a diagnostic mammogram. Most of these recalls will be false positive results. It helps to know these approximate statistics: of every 1,000 U.S. women who are screened, about 7% (70) will be called back for a diagnostic session (although some studies estimate the number closer to 10%-15%). About 10 of these will be referred for a biopsy; the remaining 60 are found to be of benign cause. Of the 10 referred for biopsy, about 3.5 will have a cancer and 6.5 will not. Of the 3.5 who do have cancer, about 2 have a low stage cancer that will be essentially cured after treatment. Mammogram results are often expressed in terms of the BI-RADS Assessment Category, often called a "BI-RADS score." The categories range from 0 (Incomplete) to 6 (Known biopsy – proven malignancy). In the UK mammograms are scored on a scale from 1-5 (1 = normal, 2 = benign, 3 = indeterminate, 4 = suspicious of malignancy, 5 = malignant).

The rates of abnormal and false-positive mammogram results are far lower in countries other than the U.S. that have adopted different quality standards. For example, in Holland, only about 1% of mammograms yield abnormal result. As a result, false-positives are much less common. Despite the higher rates of false-positives in the U.S., women are about as likely to die from breast cancer in the U.S. as in Holland and elsewhere in Europe.

While mammography is the only breast cancer screening method that has been shown to save lives, it is not perfect. Estimates of the numbers of cancers missed by mammography are usually around 10%-20%. This means that of the 350 per 100,000 women who have breast cancer, about 35-70 will not be seen by mammography. Reasons for not seeing the cancer include observer error, but more frequently it is due to the fact that the cancer is hidden by other dense tissue in the breast and even after retrospective review of the mammogram, cannot be seen. Furthermore, one form of breast cancer, lobular cancer, has a growth pattern that produces shadows on the mammogram which are indistinguishable from normal breast tissue.

Risks

The specific risks inherent in mammography are false positives, false negatives and possibly detrimental effects of radiation to the breast tissue. False positives, while they are potentially hurtful on a short term emotional basis, can usually be cleared up and fully diagnosed in one or two return visits during which more sensitive and precise tests are done. 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 can appear similar to normal tissues. Data suggests, however, that the harm from false negatives is usually slim since subsequent testing or self-breast examination (SBE) will often catch cancers that mammography misses.

The radiation exposure associated with mammography is a potential risk of screening. The risk of exposure appears to be greater in younger women. The largest study of radiation risk from mammography concluded that for women 40 years of age or older, the risk of radiation-induced breast cancer was minuscule, particularly compared with the potential benefit of mammographic screening, with a benefit-to-risk ratio of 48.5 lives saved for each life lost due to radiation exposure.[3] Organizations such as the National Cancer Institute and United States Preventive Task Force take such risks into account when formulating screening guidelines.[4]

The majority of health experts agree that the risk of breast cancer for women under 35 is not high enough to warrant the risk of radiation exposure. For this reason, and because the radiation sensitivity of the breast in women under 35 is possibly greater than in older women, most radiologists will not perform screening mammography in women under 40. However, if there is a significant risk of cancer in a particular patient (BRCA positive, very positive family history, palpable mass), mammography may still be important. Often, the radiologist will try to avoid mammography, by using ultrasound, or MRI imaging. Similarly, the risk of breast cancer to women over 55 very clearly justifies the risk of mammograms.

Regulation

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.

Mammography for transsexual women

Most of the research done on the benefits and risks of mammography has ignored the question of older transsexual women with newly acquired breasts. On the one hand, these women are often in the age where mammography shows good results in finding cancers. On the other hand, since the breast tissue is new and probably closer in density and structure to younger women’s breasts it is questionable as to how much the benefits of early detection, if indeed it’s possible given the nature of the newly formed tissue, outweigh the risks of radiation exposure. In addition, the question of hormone usage in promoting breast cancer in women with a transsexual history must be considered when deciding on what approach should be taken. Since there is no good research and a variety of opinions on what is appropriate for women with a transsexual history in relation to mammograms, the ultimate decision and responsibility will have to be shared by the trans woman herself along with her medical advisors. In any event, self-breast examination (SBE) is an easy skill should be learned by all human, transgendered humans included,

References and External Links

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