The intrinsic molecular subtypes of breast cancer are known as luminal A-like (strongly ER and PgR positive, HER2 negative, with lower proliferation markers), luminal B-like (variable degrees of ER/PgR expression, with higher proliferative fraction), HER2-enriched (ER and PgR negative, and HER2 positive) and basal-like (ER, PgR, and HER2 negative), and these are routinely used clinically to classify patients for prognostic predictions and to select treatments [17]. The gene discussed is ESR1; the disease is breast cancer.