ERBB2 and breast cancer: There are four main subtypes of BC, although different classifications exist with small differences between them: Luminal A-like (HR + /HER2 − and low-grade/low proliferation), Luminal B-like (HR + /HER2 − and high-grade/high proliferation) – luminal-like correspond to 65% of cases, HER2 + (HR + or − /HER2 +) in 15–20%, and triple negative (HR − /HER2 −) in 10–15%.