After a median follow up of 16.0 years ( IQR 14.1-17 .6 ) , 601 breast cancers have been reported ( 251 [ 7.0 % ] in 3579 patients in the tamoxifen group vs 350 [ 9.8 % ] in 3575 women in the placebo group ; hazard ratio [ HR ] 0.71 [ 95 % CI 0.60-0 .83 ] , p < 0.0001 ) .