Avoiding a False Positive on Your Mammogram

I previously wrote that mammograms are an imperfect imaging tool and do a lousy job finding breast cancers in women with dense breasts. They also may detect "false positive" abnormalities—in all women regardless of their breast density—that look suspiciously like cancer but are really benign, often necessitating an unnecessary biopsy. There are, though, ways to get a more accurate X-ray, since some mammography facilities are better than others, according to a study published this week in the Journal of the National Cancer Institute. The analysis of 44 facilities, which performed nearly half a million mammograms over five years, found that, on average, mammograms missed about 20 percent of breast cancers that were diagnosed soon after; about 10 percent of the time, they yielded a "false positive" result that later turned out not to be cancer.

But these were just averages. While the number of missed cancers didn't vary significantly among the facilities, the best of the group detected false abnormalities about 8 percent of the time compared with 12 percent of the time for the worst. What's important here is that the study researchers found particular things that differentiated the good from the not-so-good performers:

1. The best offer only screening mammograms. A facility dedicated solely to breast screening—versus one that also images breast lumps and other findings on a clinical exam—is more likely to give you an accurate finding.

2. A breast imaging specialist is on staff. This expert can help with the difficult interpretations: which suspicious shading or bright spot warrants a biopsy and which does not.

3. Radiologists don't do double readings. Having one radiologist check another's work sounds like it makes sense, but it actually increases the number of false positives.

4. The facility conducts audits two or more times per year. This is a way to ensure the quality of its machines and staff.

You might want to check to see where your facility stands before you schedule your mammogram. After all, the authors wrote, "these findings are important because a referring physician or the patient herself is much more likely to have the opportunity to choose the facility where the mammogram is performed...than they are to choose the radiologist who will interpret the mammogram."