ESR1 and breast cancer: In ER-negative patients, the mean age at breast cancer onset was considerably younger than in unselected patients: CC, 52.9 ±13.0 years (median, 53.5); CT, 50.3 ± 12.5 years (median, 49.2); TT, 50.9 ± 15.8 years (median, 48.6; p = 0.5; Figure 1b).