Adjunctive ultrasonography and cumulative incidence of advanced breast cancer in women aged 40-49 years: secondary analysis of J-START

The randomized Japan Strategic Anti-cancer Randomized Trial (J-START) found that adjunctive ultrasonography was associated with significantly higher rates of breast cancer detection than mammography alone. A prespecified secondary outcome of J-START was the long-term effect of adjunctive ultrasonography screening on the cumulative incidence of advanced breast cancer in women aged 40-49 years. The trial, at 42 study centers, included asymptomatic women without a history of breast cancer, who were randomized to ultrasonography with mammography (intervention group; n=36,723) or mammography alone (control group; n=35.938) twice during a 2-year screening period. Median follow-up for this secondary analysis was 11.4 years in the intervention group and 11.3 years in the control group. Of 894 breast cancers detected in the intervention group, 26% were advanced cancers, compared with 33% of breast cancers detected in the control group (HR 0.83; p=0.026). Kaplan-Meier curves suggested a violation of the proportional hazards assumption, with a significant difference in advanced cancer incidence only between 48 months and 96 months. Divergence between groups emerged around year four, widened until year eight, and remained stable thereafter. The authors conclude that adjunctive ultrasonography reduce the cumulative incidence of advanced breast cancer in women aged 40-40 years.