Clinically, breast cancer is classified into three basic therapeutic groups: the oestrogen receptor (ER)-positive group, the ERBB2 (also called HER2)-positive group, and the triple-negative breast cancers (TNBCs, also called basal-like), lacking expression of ER, progesterone receptor (PR) and ERBB2 (ref. 2). The gene discussed is ERBB2; the disease is breast cancer.