Follow-up mammograms may miss cancer
NEW YORK (Reuters Health) - Mammograms performed a few months after an initial mammogram shows lumps that are considered "probably benign" will often miss cancer, according to a report in the American Journal of Roentgenology.
Using data from the Breast Cancer Surveillance Consortium, Dr. Erin J. Aiello Bowles, of the Group Health Center for Health Studies in Seattle, and colleagues examined the accuracy of 45,007 follow-up mammograms interpreted 3 to 9 months after the first mammogram revealed lumps thought to be benign.
The mammograms were linked with patient characteristics and breast cancer diagnoses within 12 months. A subset of mammograms was also linked to characteristics of the radiologist who read the X-rays.
Breast cancer was diagnosed in 0.8 percent of the women within 6 months and in 1.1 percent within 12 months. Follow-up mammograms missed roughly 17 percent of the cancers diagnosed within 6 months and about 40 percent of those diagnosed within 12 months.
One reason for these findings might be that "cancers assessed as probably benign...may not grow as rapidly as cancers that appear more suspicious," the authors suggest.
Also, a radiologist who interprets the follow-up study may get a false sense of security from the fact that a colleague has already considered the first results to be "probably benign," they add.
SOURCE: American Journal of Roentgenology, May 2008.
What breastcancer.org says about this article…
Follow-up mammograms may miss cancer
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. The study reviewed here 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 Breastcancer.org Screening and Testing section to learn more about the techniques that can be used to screen for and diagnose breast cancer.
