We assessed DFS as a surrogate for OS using data from 8 randomized trials including 21 480 patients in the setting of adjuvant (post-operative) anti-HER2 therapy for patients with early HER2-positive breast cancer (Table 1).4 Individual-level surrogacy was very strong: the correlation coefficient between DFS and OS was 0.90 (95% CI: 0.89 to 0.90, unadjusted for baseline prognostic factors). This evidence concerns the gene ERBB2 and breast cancer.