Mammograms every other year do not increase the risk of breast cancer compared to yearly screening.
In 2009, the U.S. Preventive Services Task Force (USPSTF) amended its longtime recommendations for screening for breast cancer, advising women to start mammograms at age 50 instead of age 40, and to get the tests less frequently — every other year instead of yearly.
Although some studies have reported that up to 20% of breast cancers among women in their 40s could be missed under the revised USPSTF guidelines, the task force found that the risks of false positive results, over-diagnosis and unnecessary biopsies and treatment outweighed any benefit from diagnosing the few cancers among women in their 40s.
The latest study, published in JAMA Internal Medicine, evaluated the benefits and risks of the new mammography recommendations taking into account the women’s age, breast density, and postmenopausal use of hormone therapy (HT), all of which increase the risk of breast cancer. Researchers from the University of California, San Francisco analyzed data from mammogram facilities participating in the Breast Cancer Surveillance Consortium (BCSC) mammography registries from January 1994 to December 2008. Among the participants, 11,474 women had breast cancer and 922,624 women did not.
Focusing on the women’s last two mammogram screenings, the scientists concluded that women aged 50 years to 74 years who got mammograms more than 18 to 30 months apart (or every other year) showed a similar risk of advanced-stage cancer and large tumors and a lower overall risk of false-positive results than women who were screened yearly. This risk was the same regardless of their breast density or use of hormone replacement therapy, thus supporting the USPSTF’s 2009 advice in urging less frequent screening.
However, that wasn’t the case for women aged 40 to 49 with extremely dense breasts or who took estrogen and progestin therapy at menopause. Among this group, receiving screenings every other year was associated with a higher risk of discovering advanced-stage tumors than among those getting annual screenings, hinting that some potential cancers may be missed by the less frequent mammograms. The results also showed, however, that the less frequent screening produced more false-positive results.
Based on the results, the researchers concluded that the data support the recommendation that women aged 50 to 75 stick with a biennial mammogram screening schedule; the less frequent screening, they say, doesn’t lead to a significant increase in their risk of cancer. But for women in their 40s with extremely dense breasts, annual screenings may help to detect tumor earlier, but this benefit should be balanced against the risk of false-positive results that can lead to invasive biopsies, additional testing and emotional distress.
The authors write:
The 12% to 15% of women aged 40 to 49 years with extremely dense breasts, whose risk of breast cancer is similar to average-risk women aged 50 to 59 years, will need to decide if the added benefit is outweighed by the additional harms of annual screening including doubling the number of mammograms and increased risk of false-positive mammography results and breast biopsy recommendations.
“The study did surprise me,” says Laura Kruper, co-director of City of Hope’s Breast Cancer Program in Duarte, California who was not involved in the study. ”I am one of the ones saying every women must have mammogram every year at 40. This made me pause and say we need to look at this closely…We don’t have a consensus on screenings. When the task force came out with their recommendations for us to switch, it caused a huge uproar and some still advocate for annual mammograms.We have always looked at mortality as the end point, but our therapies are so good for breast cancer, that even if it is detected later on, a patient can still do well. That’s what’s great about this study–it doesn’t use mortality as the end point.”
These results aren’t likely to resolve the question of how often to screen for breast cancer, but they do provide additional information that women and their doctors should consider when deciding whether yearly, or less frequent mammograms are right for them.