Prognostication in breast cancer is routinely performed using clinico-pathologic information, namely the Nottingham Prognostic Index (NPI [86]), which comprises tumour size, grade, and lymph node status, and an IHC panel to evaluate ER, PR, and HER2 (with or without Ki67, a marker of proliferation) [87]. The gene discussed is ESR1; the disease is breast carcinoma.