ESR1 and breast carcinoma: Within the ER- cohort, HER2low breast cancer was significantly associated with increased regional nodal positivity, lower density of TILs and a lower expression of Ki-67 and epidermal growth factor receptor (EGFR) compared to HER2- cases (P < 0.001, P = 0.034, P = 0.031 and P = 0.046 respectively; Table 1).