It is the first FDA and EMA approved PI3Kα inhibitor for the treatment of PIK3CA-mutated, hormone receptor-positive (HR+), HER2-negative metastatic breast cancer, when given in combination with fulvestrant.1 Although effective in a substantial proportion of patients, adverse drug reactions (ADRs) of alpelisib are common, including hyperglycemia and skin rash. The gene discussed is PIK3CA; the disease is Skin rash.