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Follow-up Mammograms Not Reliable for About 2% of Women

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When a routine mammogram finds what seems to be a non-cancerous abnormality, doctors often order a follow-up mammogram a few months later to make sure that the abnormality is truly non-cancerous. Doctors do this because in rare cases some abnormalities that look benign will turn out to be cancer. A study found that in less than 2% of women the abnormality turned out to be cancer, and for these women the follow-up mammogram wasn't always reliable in identifying the abnormality as a true cancer.

The researchers looked at the medical histories of women who had follow-up mammograms 3 to 6 months after an earlier mammogram found what seemed to be a benign abnormality. More than 45,000 follow-up mammograms were reviewed in the study. The researchers found:

  • In slightly less than 1% of the women, the abnormality first believed to be benign was diagnosed as breast cancer within 6 months after the follow-up mammogram. In 17% of this 1% of women, the abnormality that proved to be cancer was still believed to be benign in the follow-up mammogram.
  • In 1.1% of the women, the abnormality first believed to be benign was diagnosed as breast cancer 6 to 12 months after the follow-up mammogram. In 40% of this 1.1% of women, the abnormality that proved to be cancer was still believed to be benign in the follow-up mammogram.

The good news is that during the study period, more than 98% of the women in the study were still breast cancer free after having follow-up mammograms to check on an abnormality that was thought to be benign.

Still, for about 2% of women who seemed to have a benign abnormality that was eventually diagnosed as breast cancer, follow-up mammograms were not a completely reliable way to be sure that a non-cancerous-looking abnormality is truly benign.

The researchers aren't sure why follow-up mammograms weren't more accurate at showing that a benign-looking abnormality is breast cancer. It might be that benign-looking breast cancers are less aggressive and tend to remain benign-looking in follow-up mammograms. It also might be that the doctor who interprets a follow-up mammogram is influenced by the initial classification of benign.

Interpreting mammograms and other imaging tests is not a perfect science. When the test results aren't completely clear, doctors often order more imaging tests, or different types of imaging tests. If the interpretations of the additional tests are the same, or if different imaging techniques offer the same results, doctors feel more confident that the first interpretation is correct.

If you're told that a routine mammogram has found a benign-looking breast abnormality, it's mostly likely that the abnormality is truly benign. But you should talk to your doctor about a follow-up plan that makes the most sense for you. Your doctor may recommend a follow-up mammogram to confirm that the abnormality still looks benign. You also might want to ask your doctor about the value of having a different type of breast imaging test to look at the abnormality in a different way. Breast ultrasound, MRI, and 3-D mammograms are some of the imaging options your doctor might consider. You should continue to do regular breast self-exams and have exams by a doctor when following a benign-looking breast abnormality.

Visit the Screening and Testing section to learn more about the techniques that can be used to screen for and diagnose breast cancer.

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