Breast cancer deaths were reported in 404 patients on extended tamoxifen and 452 patients in the 5-year group (RR, 0.88; P = .06).
Tamoxifen had little effect on all-cause mortality in the extended and 5-year groups (885 vs. 939 deaths; P = .2).
The aTTom study was funded by Cancer Research UK and the UK Medical Research Council. Prof. Gray reported having no financial conflicts. Dr. Partridge said she had no relevant disclosures.