Mammography - Results

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 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 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).

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 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 diagnosis (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. 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. 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. Out of 227 cancers found, the CAD method found just one fewer than the 199 cancers found using two separate physicians.