Luminal A is defined by IHC by positivity to any hormone receptor (estrogen receptor (ER) or progesterone receptor (PR)) negativity to HER2 and a KI-67 staining in <14% of tumour cells; Luminal B is defined by positivity to any hormone receptor and a Ki-67 staining ≥ 14%; HER2 subtypes present negativity to both hormone receptors and positivity to HER2 and triple-negative breast cancers (TNBC) present negativity to both hormone receptors and HER2. The gene discussed is ERBB2; the disease is neoplasm.