OS outcome
compared to the original TAM01 trial, and according to the ITT principle, the OS endpoint did not achieve statistical significance. When implementing an unadjusted Cox model, the relative hazards comparing the extended tamoxifen group and the ST group were 0.94 (0.84–1.07) in all cohort and 0.93(0.80–1.09) in ER positive women. The counterfactual statistical methods revealed that the observed survival benefit was likely to be underestimated (Fig. 