Women aged 50 to 74 years who undergo screening mammography every other year, even those with high breast density or a history of hormone therapy after menopause, appear no more likely to be diagnosed with advanced-stage breast cancer than comparable women who are screened annually. They also have a lower risk of receiving false-positive results, which means they are less likely to undergo unnecessary tests, such as additional imaging or a biopsy, according to findings appearing today in JAMA Internal Medicine.
In addition, the study found that for women aged 40 to 49 years with extremely dense breasts who are considering mammography, annual examinations may minimize their risk of advanced-stage disease, but they have a greater chance of experiencing false-positive results.
The findings were based on an analysis of data collected prospectively on 11 474 women with breast cancer and 922 624 without breast cancer who underwent mammography at facilities participating in the Breast Cancer Surveillance Consortium.
Lead author Karla Kerlikowske, MD, of the University of California, San Francisco, discusses her team’s findings:
news@JAMA: The US Preventive Services Task Force already recommends biennial screening mammography for women aged 50 to 74, so why did you do the study?
Dr Kerlikowske: The task force’s recommendation was strictly based on age. We asked ourselves if there are some high-risk women, such as those with dense breasts or who had hormone therapy, for whom annual mammography would be beneficial. We did not find any additional benefit with annual mammography. It’s very reassuring and tells you something about how tumors grow pretty slowly even in women with these risk factors.
news@JAMA: The task force also recommended that the decision to start biennial screening mammography before age 50 should be an individual one, taking into account such elements as the patient’s values regarding specific benefits and harms. But your analysis found that in younger women who also have extremely dense breasts, biennial screening increased the risk of detecting advanced-stage cancer by almost 90% compared with annual screening. So what would you tell women entering their 40s who are considering breast cancer screening for the first time but who yet do not know their breast density because that can only be determined through mammography?
Dr Kerlikowske: First of all, I agree with the task force recommendations. But if I’m seeing a woman considering screening, I’d first ask her if she has already some risk factors like a family history. If she does, I may suggest she get a mammogram, which would also establish her breast density. However, the downside to annual mammography is increased false positives. About two-thirds of women with extremely dense breasts who undergo annual mammography will, at some time in a 10-year period, have a false positive. With a 2-year screening interval, that chance of a false positive over a 10-year period drops to about 40%.
news@JAMA: What are the downsides of false positives?
Dr Kerlikowske: For mammograms, the downsides include the need for additional imaging, which increases radiation exposure. They are an inconvenience to women and can cause short-term and even longer-term anxiety. They also lead to false-positive biopsies, and studies have shown the more biopsies you have decreases the specificity of mammogram, making you at even more at risk of future false positives.