ESR1 and breast cancer: During the 10.5 years (τ=10.5), the mean life lost due to death from breast cancer was 0.9 (S0) years for patients in the ER-positive group and 2.4 (S0+S1) years for patients in the ER-negative group, and ER-negative patients lost an additional 1.5 (2.4–0.9) years of life on average.