New Studies Evaluate Breast Cancer Screening
In conjunction with the release of the US Preventive Services Task Force updated recommendations for breast cancer screening, three research articles analyzing the effectiveness and harms of screening were published in the Annals of Internal Medicine by investigators at the Pacific Northwest Evidence-based Practice Center at Oregon Health & Science University (OHSU).

"Our goal was to analyze research on the effectiveness of mammography screening in reducing advanced breast cancer, breast cancer death, and death from all causes for women at average risk of breast cancer, as well as determining the frequency of potential harms from screening," says Heidi D. Nelson, MD, MPH, first author on the studies. "In addition, we analyzed how effectiveness and harms vary by age, risk factors, screening intervals, and screening methods."

Nelson is a research professor of medical informatics and clinical epidemiology and medicine in the OHSU School of Medicine, a member of the Knight Cancer Institute at OHSU, and medical director of cancer prevention and screening at Providence Health & Services Oregon.

The systematic reviews conducted by Nelson and colleagues are summarized below:

Effectiveness of Breast Cancer Screening: Systematic Review and Meta-Analysis to Update the 2009 US Preventive Services Task Force Recommendation
The study determined the effectiveness of breast cancer screening in average-risk women by evaluating results of randomized controlled trials and observational studies. The meta-analysis of updated results of screening trials indicated that breast cancer mortality was generally reduced with screening compared with nonscreening, although differences were not statistically significant for women aged 39 to 49 and 70 to 74.

"Our meta-analysis of screening trials also indicated that advanced cancer was reduced with screening for women aged 50 and older, but not for younger women," Nelson says.

Harms of Breast Cancer Screening: Systematic Review to Update the 2009 US Preventive Services Task Force Recommendation
The study summarized studies of potential screening harms, including false-positive results, overdiagnosis, anxiety, pain, and radiation exposure. Overdiagnosis refers to receiving a diagnosis of ductal carcinoma in situ or invasive breast cancer that is unlikely to become clinically evident during a woman's lifetime in the absence of screening.

Based on two studies of US data, 10-year cumulative rates of false-positive mammography results and biopsies were higher with annual rather than biennial screening (61% vs 42%, and 7% vs 5%, respectively), and for women aged 40 to 49 years, those with dense breasts, and those using combination menopausal hormone therapy. Women with false-positive results were more likely to have additional imaging tests and biopsies, and in studies, they reported more anxiety, distress, and breast cancer-specific worry, although results varied.

"While overdiagnosis is an important potential harm of screening, it is difficult to determine and apply to individual women, and estimates are based on many different methods and data sources," Nelson says. "As a result, the actual rate of overdiagnosis is not clear."

Descriptive studies showed that some women experience pain with mammography and are discouraged from future screening. Statistical models indicated that deaths due to radiation exposure from screening are rare.

Factors Associated With Rates of False-Positive and False-Negative Results From Digital Mammography Screening: An Analysis of Registry Data
This study determined the factors associated with false-positive and false-negative screening results among a general population of women screened for breast cancer in the United States.

Data based on results from a single screening round for women regularly screened with digital mammography indicated that false-positive results were common in all age groups. Data collected between 2003 and 2011 from the Breast Cancer Surveillance Consortium—a collaborative network of mammography registries across the United States that is supported by the National Cancer Institute—indicated that the rate of false-positives was highest among women aged 40 to 49 years and decreased across older age groups. Results did not differ by whether women were last screened one vs two years ago.

"Our research found that false-positive mammography results are common, while false-negatives are low," Nelson says. "False-positive rates were particularly high for younger women and those with risk factors, including family history of breast cancer, previous benign breast biopsy, high breast density, and low body mass index—younger women only."

"The results of these studies may be useful for women and clinicians considering the individual benefits and harms of screening, in addition to health service administrators responsible for screening programs in populations," Nelson adds.