Several key prognostic factors for BC include the expression of estrogen receptor α (ERα), which distinguishes tumors as ERα-positive or ERα-negative, the status of breast cancer type 1 susceptibility protein (BRCA1) (wild type—wt versus mutated), and the expression of progesterone receptor (PR) and HER2, further dividing different subgroups within the LumA and LumB phenotypes. The gene discussed is BRCA1; the disease is breast cancer.