A study of 1.5 million women concluded that universal biennial mammography is more effective for detecting breast cancer early compared with risk-based screening or annual clinical breast exam (CBE).

Most evaluations of mass screening for breast cancer have focused on a single detection method, and very few studies have been conducted to address comparisons of benefits and harms across different detection methods, especially in the same population. Although universal mammography screening is the most widely adopted approach to population-based screening, comparative effectiveness research focused on different screening strategies is still important owing to the enduring debate over the value of mammography screening.

Published by JAMA Oncology, led by Amy Ming-Fang Yen, PhD, and performed in the National Taiwan University Hospital, the study featured a large, population-based cohort to clarify concerns about limited benefits and excessive harms and to explore the possibility of alternative approaches to reduce avoidable deaths from breast cancer.

A total of 1.5 million asymptomatic women attending outreach screening in the community or undergoing mammography in hospitals were enrolled in the three screening programs that included risk-based biennial mammography where only woman at high risk were screened, universal biennial mammography where all women were screened, and annual CBE where there was no mammography, just an examination.

The aim of this study is to present basic background information, screening performance data, and outcomes of each screening program, and to compare effectiveness in reducing advanced stages of breast cancer, death from breast cancer, and the estimates of overdiagnosis associated with each screening strategy.

Overall, the detection rates (prevalent screenings and subsequent screenings per 1,000) were highest for universal biennial mammography (4.86 and 2.98, respectively), followed by risk-based biennial mammography (2.80 and 2.77, respectively) and lowest for annual CBE (0.97 and 0.70, respectively). Universal biennial mammography was the most effective strategy for detecting breast cancer early: it achieved a 40 percent mortality reduction through the reduction in stage II+ disease.

In contrast, implementation of risk-based mammography screening, while seemingly pragmatic in the presence of limited resources, resulted in only a small benefit compared with CBE. Universal biennial mammography screening also was associated with only a modest level of overdiagnosis.

The significant mortality reduction revealed in this study supports the use of mammography for mass breast cancer screening in a country with a low but increasing trend in breast cancer incidence. The findings are further support for the benefits of mammography screening reported in most systematic reviews and meta-analyses.

The study also confirms that mammography screening with good quality control is reproducible in organized breast cancer service screening programs implemented in countries with low or intermediate incidence but increasing incidence trends. “The findings on overdiagnosis also indicate that little harm is caused by universal biennial mammography screening. These findings are consistent with previous studies with adjustment for lead time but at odds with the highly elevated estimates of overdiagnosis attributable to mammography screening when there has been no adjustment for lead time” wrote Yen.