Biennial mammography starting at age 40 prevented more breast cancer deaths than starting at age 50 while maintaining a balanced rate of screening harms, according to an analysis commissioned by the U.S. Preventive Services Task Force.
Researchers found that screening every other year from ages 40 to 74 prevented about eight breast cancer deaths per 1,000 women screened and added 165 life-years. This strategy resulted in approximately 1,376 false-positive findings and 14 overdiagnosed cases per 1,000 patients. Compared with initiating screening at 50, starting at 40 prevented up to 19% more deaths, with only modest increases in false positives and overdiagnosis.
When comparing annual and biennial intervals, annual screening beginning at 40 prevented two additional deaths per 1,000 women but produced substantially more harms, including roughly 15,000 additional mammograms, 700 more false-positive recalls, 87 more benign biopsies, and seven more overdiagnosed cases. The U.S. Preventive Services Task Force (USPSTF) recommended biennial mammography beginning at age 40 and continuing through 74 for patients at average risk.
The modeling analysis evaluated 18 screening strategies that varied by starting and stopping age and screening interval. Data inputs included performance characteristics of digital mammography and digital breast tomosynthesis, as well as breast cancer incidence, tumor biology, stage at diagnosis, and survival outcomes under contemporary treatment.
Evidence from randomized controlled trials conducted from the 1960s to the 1990s demonstrated a 14% to 32% reduction in breast cancer mortality among women aged 50 to 69 years. These findings provided the foundation for modern screening recommendations despite pre-dating current therapies and imaging methods.
“Randomized controlled trials establish the foundational scientific evidence of the benefit of screening mammography in reducing breast cancer mortality,” said Zahir Kanjee, MD, MPH, Beth Israel Deaconess Medical Center, 330 Brookline Avenue, Boston, Massachusetts, and colleagues.
The researchers noted that older trial data limited the precision of mortality estimates because current screening and treatment options differ from those historically available. Modeling results depended on assumptions about cancer progression, test sensitivity, and treatment effects. Uncertainty also remained around the rates of false positives and overdiagnosis, which varied across studies.
Overall, biennial screening beginning at age 40 provided the most favorable balance between mortality reduction and screening-related harms for women at average risk. Earlier or more frequent screening offered slight mortality improvements but increased unnecessary imaging and biopsies. The USPSTF emphasized shared decision-making between physicians and patients when selecting a screening approach that reflects individual risks and preferences.
All financial relationships among study authors were reported and mitigated.
Source: Annals of Internal Medicine
