Women diagnosed with breast cancer who had regular screening mammograms every year were less likely to have late-stage cancer and had a higher overall survival rate than women who had screenings every two years or less frequently, according to a new study from the University of Pittsburgh and UPMC published in Journal of Clinical Oncology.

“Only about 65% of women over 40 are screened for breast cancer, and only about half of those women attend screening annually — in part because of conflicting guidelines on recommended screening intervals,” said lead author Margarita Zuley, MD, professor and chief of the Breast Imaging Section in the Department of Radiology at Pitt and UPMC. “Our study shows that annual screening provides a significant benefit over biennial screening, even in premenopausal women.”

Although many clinical trials have demonstrated the benefits of mammography screening for breast cancer, there are varying guidelines on how often women should be screened. The American College of Radiology and several other organizations recommend annual screening starting at age 40, while the U.S. Preventive Services Task Force recommends biennial screening starting at age 40.

Because there is no national breast cancer registry in the United States, Zuley and her team recently developed a large institutional database to better understand the true outcomes for breast cancer patients.

To gain more insight into optimal mammography screening intervals, researchers used this database to compare 8,145 breast cancer patients who had at least one mammogram before diagnosis. The screening interval was considered annual if the time between mammograms was less than 15 months, biennial if it was between 15 and 27 months, and intermittent if it was more than 27 months.

The proportion of advanced cancer (TNM stage IIB or worse) was 9%, 14%, and 19% in the annual, biennial, and intermittent screening groups, respectively. The biennial and intermittent groups had significantly worse overall survival than the annual group.

“The proportion of late-stage cancers increased significantly as screening intervals increased,” Zuley said. “Annual mammograms are critical for early detection of breast cancer. They increase the chance of survival, reduce harm to patients because treatment may not need to be as intensive, facilitate recovery, and can reduce the cost of treatment.”

A problem with more frequent mammograms is the increased risk of false positive results, leading to unnecessary biopsies and anxiety.

“We recognize that there is potential harm in calling women back for additional screenings, but I don’t believe those harmful effects outweigh the risk of missing cancers and causing women to die from them,” Zuley said. “We are also working to test screening methods that have fewer false positives than mammograms and are working on all fronts to find the most cost-effective and accurate way to care for our patients.”

Other authors of the study were Andriy Bandos, Ph.D., Durwin Logue, Rohit Bhargava, MD, Priscilla McAuliffe, MD, Ph.D., Adam Brufsky, MD, Ph.D., and Robert M. Nishikawa, Ph.D., all of Pitt and UPMC; and Stephen Duffy, Ph.D., of Queen Mary University of London.