External validity of breast cancer screening in East Asia: An evidence-informed policy framework for supplemental ultrasound in Korea

Korea's National Cancer Screening Program has provided biennial mammography for women aged 40–69 for over two decades, yet breast cancer mortality has risen continuously since 1983, contrasting with 20–43% reductions in Western countries. This mortality paradox reflects a fundamental external validity failure: mammography-only guidelines developed for Western populations, where most women do not have dense breasts, are applied authoritatively to Korea, where 83% of women do. Dense breast tissue reduces mammography sensitivity to 47–68%, below acceptable performance thresholds, while conferring 3- to 5-fold higher cancer risk and 17-fold higher interval cancer rates. Evidence on supplemental ultrasound was synthesized across four domains—population context, clinical effectiveness, implementation feasibility, and economic considerations—using an evidence-informed public health framework. A population-stratified meta-analysis demonstrates an eleven-fold more favorable specificity trade-off for supplemental ultrasound in East Asian versus Western women. J-START ( n = 72,998) showed that supplemental ultrasound increased sensitivity from 77% to 91% and halved interval cancers in women aged 40–49. The USPSTF’s dismissal of J-START's interval cancer reduction as non-significant relies on selective analysis of invasive cancers only; including all interval cancers yields a statistically significant result (RR 0.50, 95% CI 0.29–0.88). Cost-effectiveness evidence supports feasibility. Three implementation pathways—universal, age-targeted, and risk-stratified—are mapped to Korean population data with explicit equity-efficiency trade-offs. Continued uncritical application of Western guidelines constitutes a systematic failure of equity for 83% of Korean women; phased implementation with prospective monitoring is both evidence-supported and an equity imperative.