More mammograms, more false positives

First it was PSA tests, now yearly mammograms are causing controversy among experts. According to a new study published in this week’s online Annals of Internal Medicine, more than half of all women who have annual testing starting at age 40 will be called back for more testing thanks to a false positive.

How did researchers arrive at that number? The study, funded by the U.S. National Cancer Institute, involved nearly 170,000 women who had their first mammograms between the ages of 40-59 years (during the period from 1994-2006) and about 4500 women diagnosed with incident invasive breast cancer between 1996 and 2006.

The results? After a decade of annual screenings, experts found that about 60 per cent of women had at least one false positive. Forty per cent women who had the test biennially — that is, every other year — also had a false positive within the same time frame. Seven to nine per cent of women who went on to have biopsies also had a false positive.

In other words, if you have a mammogram once a year for ten years, there’s a good chance you’ll have a false positive somewhere along the line. If you go every other year, you’re less likely to experience a false positive. The results don’t seem surprising — it stands to reason that the more often a test is performed, the greater the chance they’ll be an error at some point.

So what are experts recommending? Researchers say that having a mammogram every other year decreases the chance of receiving a false positive, but admit there’s a catch — it could delay a crucial cancer diagnosis. As we know, the earlier a cancer is caught, the better.

So if experts aren’t changing their recommendations, what’s the point? Women should be better informed about the potential for error.

“We conducted this study to help women know what to expect when they get regular screening mammograms over the course of many years,” said study leader Rebecca Hubbard, an investigator at Group Health Research Institute of Seattle, in a statement.

“We hope that if women know what to expect with screening, they’ll feel less anxiety if — or when — they are called back for more testing. In the vast majority of cases, this does not mean they have cancer.”

The study didn’t include false negatives or evaluate the effectiveness of different types of mammography.

Read the abstract, and see CBC News for more information.

Recommendations in Canada

Currently, all provincially organized screening programs in Canada advise women between the ages of 50-69 to get regular screenings, according to the Canadian Breast Cancer Foundation. (Guidelines for women under age 50 or over age 70 differ by province.) There is some evidence to suggest that women in their forties can benefit from regular screenings — especially if they are at a higher risk for the disease. However, experts recommend women talk to their doctor about their risks of developing the disease and the pros and cons of testing.

Overall, the message is not to skip screenings. Women know mammograms aren’t particularly enjoyable or comfortable, but they can help save lives — even if there’s a mistake from time to time.


For more information about breast cancer, visit the Canadian Breast Cancer Foundation and the Canadian Cancer Society.

To read more about breast cancer, see our previous articles:

Everyday ways to prevent breast cancer
The Zoomer Report: Mammography Latest
Top health issues affecting women

Photo © Catherine Yeulet