False Positive Mammograms & Subsequent Breast Cancer Risk

A recent study points to a higher risk of breast cancer in women with a history of a false positive mammogram.

Investigators examined the number of breast cancers occurring over 10 years with whose routine screening mammogram had resulted in either a “call back” normal mammogram or a benign breast biopsy (false positive mammograms), and compared it to the number of cancers in women whose mammogram was normal on the first go round (true negative mammogram.)

Women who had a false positive mammogram had a higher risk of breast cancer in the subsequent 10 years compared to women with a true negative mammogram. How much higher? As you can see in the graph above, for every 1/000 women with a true negative mammogram, 3.9 breast cancers occurred within the subsequent 10 years. This is in contrast to women with false positive mammograms who had 5.5 breast cancers for every 1,000 women, and women with a false positive biopsy who had 7 cancers per 1,000 women.

Thought the relative risks between groups is statistically significant, it’s extremely important to realize that ALL these risks are under 1%, so we are making distinctions between very small numbers.

Here’s what the study results looks like in an icon array, a useful tool for illustrating comparative risks that are under 1%. Among the 1,000 women pictured in each array below, the pink ladies are the ones who developed breast cancer within the 10 years, while the grey ladies remain cancer free.

Further stratifying results by breast density, the researchers found that 10 year subsequent breast cancer risk was highest in women with extremely dense breasts and a false positive biopsy (9.01 per 1,000 women), and lowest in women with fatty breasts and true negative mammograms (2.22 per 1,000 women), with the rest scattered in between according to density.

The investigators uses data from the Breast Cancer Surveillance Consortium (BCSC) from 1994 to 2009, studying over 2 million mammograms done in over 1 million women. It’s a robust database that the US Preventive Services Task Force used to advise their recommendations for mammogram screening. They adjusted risk data for age, race/ethnicity, menopausal status, history of breast biopsy, and family history of breast cancer, all factors that are associated with breast cancer risk.  The study results are consistent with those of other studies, adding to a growing body of literature linking false positive mammograms with breast cancer risk.

Now What?

A history of a prior breast biopsy is a known risk factor for subsequent breast cancer, and is already incorporated into the Gale Model and other breast cancer risks assessment tools. It may be time to consider incorporating a history of a prior false positive mammogram into these tools. At this point, breast density has not been incorporated into these risks assessment tools, primarily because it is such a subjective measure with not great reproducibility, and because it changes over time.

How to Use This Information

Women and their doctors may want to use this information to help them decide how often to have mammograms, or whether or not to begin to incorporate sonograms into their breast cancer screening regimen.

That said, it’s important to understand that although the risks for breast cancer are increased by a false positive mammogram, the absolute increase in risk is modest – still less than 1% in even the highest risk group.