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MammographyÂ is the process of using low-dose amplitude-X-rays (usually around 0.7Â mSv) to examine the humanÂ breastÂ and is used as a diagnostic and a screening tool. The goal of mammography is the early detection ofÂ breast cancer, typically through detection of characteristic masses and/or microcalcifications. Mammography is believed to reduce mortality fromÂ breast cancer. Remaining aware of breast changes and physician examination are considered essential parts of regular breast care.In many countries routine mammography of older women is encouraged as a screening method to diagnose early breast cancer. In 2009, the U.S. Preventive Services Task Force issued a dramatic change in the mammography guidelines for women between the ages of 40 and 49. In short, the USPSTF recommended that women begin having mammograms at age 50, instead of the previous 40-years-of-age starting point. This shift in government guidelines was met with swift negative reaction by several cancer and women's organizations. Nonetheless, theÂ USPSTFÂ still recommends screening mammography, with or without clinical breast examination, every 2 years for women aged 50 to 74.Â Altogether clinical trials have found a relative reduction in breast cancer mortality of 20%.Â Mammograms have been controversial since 2000, when a paper highlighting the results of the two highest-quality studies was published.
Like all x-rays, mammograms use doses ofÂ ionizing radiationÂ to create images.Â RadiologistsÂ then analyze the image for any abnormal findings. It is normal to use longerÂ wavelengthÂ X-rays (typically Mo-K) than those used forÂ radiographyÂ ofÂ bones.
At this time, mammography along with physical breast examination is the modality of choice for screening for earlyÂ breast cancer.Â Ultrasound, ductography, positron emission mammography (PEM), andÂ magnetic resonance imagingÂ are adjuncts to mammography.Â UltrasoundÂ is typically used for further evaluation of masses found on mammography or palpable masses not seen on mammograms. Ductograms are still used in some institutions for evaluation of bloody nipple discharge when the mammogram is non-diagnostic.Â MRIÂ can be useful for further evaluation of questionable findings as well as for screening pre-surgical evaluation in patients with known breast cancer to detect any additional lesions that might change the surgical approach, for instance from breast-conservingÂ lumpectomyÂ toÂ mastectomy. New procedures, not yet approved for use in the general public, including breastÂ tomosynthesisÂ may offer benefits in years to come.
Breast self-examinationÂ (BSE) was once promoted as a means of finding cancer at a more curable stage, however, it has been shown to be ineffective, and is no longer routinely recommended by health authorities for general use.Awareness of breast health and familiarity with one's own body is typically promoted instead of self-exams.
Mammography has a false-negative (missed cancer) rate of at least 10 percent. This is partly due toÂ denseÂ tissues obscuring the cancer and the fact that the appearance of cancer on mammograms has a large overlap with the appearance of normal tissues.
During the procedure, the breast is compressed using a dedicated mammography unit. Parallel-plate compression evens out the thickness of breastÂ tissueÂ to increase image quality by reducing the thickness of tissue that x-rays must penetrate, decreasing the amount of scattered radiation (scatter degrades image quality), reducing the required radiation dose, and holding the breast still (preventingÂ motion blur). In screening mammography, both head-to-foot (craniocaudal, CC) view and angled side-view (mediolateral oblique, MLO) images of the breast are taken. Diagnostic mammography may include these and other views, including geometrically magnified and spot-compressed views of the particular area of concern.Â Deodorant,Â talcum powderÂ orÂ lotionÂ may show up on the X-ray asÂ calciumÂ spots, and women are discouraged from applying these on the day of their exam.
Until some years ago, mammography was typically performed with screen-film cassettes. Now, mammography is undergoing transition to digital detectors, known asÂ digital mammographyÂ or Full Field Digital Mammography (FFDM). The first FFDM system was approved by the FDA in the U.S. in 2000. This progress is some years later than in general radiology. This is due to several factors:
the higher spatial resolution demands of mammography,
significantly increased expense of the equipment,
concern by the FDA that digital mammography equipment demonstrate that it is at least as good as screen-film mammography at detecting breast cancers without increasing breast dose or the number of women recalled for further evaluation.
As of March 1, 2010, 62% of facilities in the United States and its territories have at least one FFDM unit.(The FDA includes computed radiography units in this figure.)
In order to encourage the use of mammograms as a screening measure for breast cancer, a number of hospitals, cancer centers and other healthcare groups have started mobile mammography vans to bring affordable, accessible and convenient mammograms to their communities. Many mobile mammography vans prioritize serving uninsured, low-income and/or non-English-speaking women who otherwise could not otherwise afford a mammogram or who are unaccustomed to seeing a doctor. Many offer free or low-cost mammograms to women who are uninsured and/or cannot afford a mammogram.
In the past several years, the "work-up" process has become quite formalized. It generally consists of screening mammography, diagnostic mammography, andÂ biopsyÂ when necessary, often performed viaÂ stereotactic core biopsyÂ orÂ ultrasound-guided core biopsy. After a screeningÂ 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 by a technologist. Depending on the nature of the finding,Â ultrasoundmay often be used at this point, as well.
Generally the cause of the unusual appearance is found to beÂ 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 theÂ pathologistÂ to examine microscopically to determine the precise cause of the abnormality. In the past, biopsies were most frequently done in surgery, under local or generalÂ 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. TheseÂ core biopsiesÂ require only local anesthesia, similar to what would be given during a small dental procedure.
Often women are quite distressed to be called back for a diagnostic mammogram. Most of these recalls will beÂ false positiveÂ 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 individuals 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 have cancer, about 2 have a low stage cancer that will be essentially cured after treatment. Mammogram results are often expressed in terms of theÂ BI-RADSAssessment Category, often called a "BI-RADS score." The categories range from 0 (Incomplete) to 6 (Known biopsyÂ - 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).
Mammography may also produce false negatives. Estimates of the numbers of cancers missed by mammography are usually around 10%-30%. This means that of the 350 per 100,000 women who have breast cancer, about 35-105[Â will not be detected by mammography. Reasons for not seeing the cancer include observer error, but more frequently it is because 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.
Computer-aided diagnosisÂ (CAD) are being tested to decrease the number of cases of cancer that are missed in mammograms. In one test, a computer identified 71% of the cases of cancer that had been missed by physicians. However, the computer also flagged twice as many non-cancerous masses than the physicians did. In a second study of a larger set of mammograms, a computer recommended six biopsies that physicians did not. All six turned out to be cancers that would have been missed.Â Generally, CAD systems in screening mammography have poor specificity and compare poorly to double reading.
While data are accumulating suggesting that CAD can find a few additional cancers, this should be put in perspective. The additional find rate was 20%, thus in a group of 10,000 women who will have about 40 cancers, CAD may help find an additional 8. The types of additional cancers that may be found are likely to be early and small.Â As of 2006, there have been no data to show that finding these additional cancers will have any effect on survival rate. Some feel that these cancers are likely to be found at the next screening, still at a curable stage, and therefore it remains to be proven whether CAD will be eventually found to have any effect on patient outcome.
A study released October 1, 2008, by British researchers revealed that using CAD in conjunction with a single reading by a physician may be as beneficial as a second reading by a physician. The study of 31,000 women, the largest of its kind to date, determined that the find rate for a single physician in conjunction with CAD as compared to two physicians was nearly identical.Â Out of 227 cancers found, the CAD method found just one fewer than the 199 cancers found using two separate physicians.
The goal of any screening procedure is to examine a large population of patients and find the small number most likely to have a serious condition. These patients are then referred for further, usually more invasive, testing. Thus a screening exam is not intended to be definitive: It is intended to have a high sensitivity so as to not miss any cancers. The cost of this high sensitivity is a relatively large number of results that would be regarded as suspicious in patients without disease. This is true of mammography. The patients called back for further testing from a screening session (about 7%) are sometimes referred to as "false positives", implying an error. In fact, it is essential to call back many healthy patients for further testing to capture as many cases of cancer as possible.
Research showsÂ that false-positive mammograms may affect women's well-being and behavior. Some women who receive false-positive results may be more likely to return for routine screening or perform breast self-examinations more frequently. However, some women who receive false-positive results become anxious, worried and distressed about the possibility of having breast cancer, feelings that can last for many years.
At the same time, mammograms also have a rate of missed tumors, or "false negatives." Accurate data regarding the number of false negatives are very difficult to obtain, simply becauseÂ mastectomiesÂ cannot be performed on every woman who has had a mammogram to determine the false negative rate accurately. Estimates of the false negative rate depend on close follow-up of a large number of patients for many years. This is difficult in practice, because many women do not return for regular mammography making it impossible to know if they ever developed a cancer. Dr. Samuel S. Epstein, in his book,Â The Politics of Cancer, claims that in women ages 40 to 49, one in four instances of cancer is missed at each mammography. Researchers have found that breast tissue is denser among younger women, making it difficult to detect tumors. For this reason, false negatives are twice as likely to occur in premenopausal mammograms(Prate.) This is why the screening program in the UK does not start calling women for screening mammograms until the age of 50.
The importance of these missed cancers is not clear, particularly if the woman is getting yearly mammograms. Research on a closely related situation has shown that small cancers that are not acted upon immediately, but are observed over periods of even several years, will have good outcomes. A group of 3,184 women had mammograms which were formally classified as "probably benign." This classification is for patients who are not clearly normal but have some area of minor concern. This results, not in the patient being biopsied, but having early follow up mammography every six months for three years to guarantee no change. Of these 3,184 women, 17 (0.5%) did have cancers. Most importantly, when the diagnosis was finally made, they were all still stage 0 or 1, the earliest stages. Five years after treatment, none of these 17 women had evidence of recurrence. Thus, small early cancers, even though not acted on immediately, were still entirely curable.
CRITIQUE OF SCEENING MAMMOGRAPHY
The use of mammography as a screening tool for the detection of early breast cancer continues to be debated. Critics point out that a large number of women need to be screened to find cancer. Kopans reminds us that since 1990, the death rate from breast cancer has decreased by almost 30% and points to studies in Sweden and the Netherlands that show two-thirds of the decrease in cancer deaths is due to mammography screening.Â Keen and Keen indicated that repeated mammography starting at age 50 saves about 1.8 lives over 15 years for every 1,000 women screened.Â This result has to be seen against the negatives of errors in diagnosis,Â overtreatment, and radiation exposure. Countercritics argue that the benefit is greater. The Cochrane analysis of screening indicates that it is "not clear whether screening does more good than harm". According to their analysis one in 2,000 women will have her life prolonged by 10 years of screening, however, another 10 healthy women will undergo unnecessary breast cancer treatment. Additionally, 200 women will suffer from significant psychological stress due to false posivitive results.Â Newman points out that screening mammography does not reduce death overall, but causes significant harm by inflicting cancer scare and unnecessary surgical interventions.Â Finally, a significant recent article points out that a successful screening program should result in an increase in the number of early breast cancers, followed by a decrease in the number of late-stage cancers. However this is not happening with current mammography screening.