ESR1 and breast cancer: (60) 350 female canine mammary cancers were classified as luminal A (14.3%), luminal B (9.4%), no HER2-overexpressing and triple-negative (76.3%) either of the basal-like type (ER- and PR-, EGFR and/or CK5/6+) (58.6%) or of the non-basal-like type (ER- and PR-, EGFR, and CK5/6-) (17.7%) (60).