Tumours produced when several thousand KRASG12D–transduced BCs or LPs are transplanted into immunodeficient mice are highly polyclonal, histologically classified as invasive ductal carcinomas (IDCs) but phenotypically heterogeneous, with a variable content of cells positive for oestrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor-2 (HER2), EGFR, Ki67 and cytokeratins (CK) 8/18 [10]. The gene discussed is ERBB2; the disease is invasive ductal breast carcinoma.