Breast cancer is routinely characterised immunohistochemically by the expression of receptors such as HER2, ERα, PgR and EGFR; gene expression profiling can also be used to identify molecular characteristics of breast cancer cells and classify them into 5 specific subtypes with distinct clinical outcomes: luminal A, luminal B, HER2-overexpressing, basal and normal-like tumours [46, 47]. The gene discussed is PGR; the disease is breast carcinoma.