Why Mammograms Are Less Effective Among Breast Cancer Survivors

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Steve Smith

Sometimes, even in medicine, where it’s all about evidence, we slip and take some things for granted. Such as, for instance, the fact that women who have survived breast cancer should get regular mammogram screenings, so they and their doctors can stay ahead of any potential recurrent tumors.

It makes sense. After all, women who have had breast cancers are much more likely to experience either re-growths or new malignancies compared with women who have never had the disease. And mammography lowers the risk of breast cancer among healthy women, so it must do same for those who have had tumors removed. (More on Time.com: Why British Doctors May Read Mammograms Better)

Yet a new study found that’s not the case. Pooling data from several of the U.S.’s cancer registries, scientists found that mammography did not catch as many tumors among women with a history of cancer as it did among those who have never had the disease.

The researchers measured the number of cancers detected among women within a year of a first screening. Compared to matched controls, women with a history of breast cancer had nearly three times as many cancers detected. But the sensitivity of the mammograms in picking up these growths was about 65% among these women, compared to 76% in women without breast cancer.

There could be several reasons for why mammograms weren’t as effective in picking up cancers in breast cancer patients, says Diana Miglioretti, an investigator with the Group Health Research Institute in Seattle and a co-author of the study. First, she says, women who have survived breast cancer are more likely to be more vigilant about looking for future growths, and are probably doing more self-examinations to detect any abnormal tumors. If these women were finding such cancers, they would count as being missed by mammography, lowering the sensitivity of the screen. (More on Time.com: Some Women May Not Need Lymph Node Surgery)

In addition, among women with a history of breast cancer, mammograms tended to be better at picking up localized growths in breast tissue, known as ductal carcinoma in situ (DCIS) as opposed to invasive cancer. That’s because mammograms are X-ray based, and are better at detecting the calcifications associated with DCIS, as opposed to the invasive cancers, which are embedded in soft tissues. Survivors of cancer are more likely to develop metastases, which are more invasive, than women without a history of the disease, which could also explain mammography’s weaker sensitivity among cancer survivors.

Still, says Miglioretti, the results shouldn’t discourage breast cancer patients from getting regular mammograms. In fact, the findings highlight the fact that mammography may be missing some intervening cancers, which suggests the need for closer evaluation of breast tissue in this population.

“Women need to remain vigilant, and go see their doctor if they are concerned about changes in their breast,” she says. “Some groups of women who have dense breast tissue, or are younger, are more likely to have interval cancers. We don’t know why mammography is missing these cancers, but the next study will need to look at possible alternative screening strategies for these women.” (More on Time.com: Why Those Agonizing Hot Flashes May Not Be All Bad)

It never hurts, she says, to stay ahead of any recurrent or new growths, and if mammograms aren’t the best way to do that, then women should talk to their doctors about trying other options for detecting future growths.