ESR1 and breast cancer: In multivariate analysis adjusting for tumor size, tumor grade, lymph node status, ER/PR status, and Her2 overexpression, Nuc-Stat5a remained an independent marker of survival in Material VI, predicting a fivefold increased risk of breast cancer-related death (CSS; multivariate Cox regression HR = 4.95 (1.87, 13.06); P = 0.001; n = 55; Table 3).