Abstract
Capivasertib is a serine/threonine kinase AKT (AKT1–3) inhibitor, disrupting phosphorylation of AKT substrates. When combined with fulvestrant, it is approved for hormone receptor‐positive advanced breast cancer. Capivasertib therapy frequently causes hyperglycemia, including diabetic ketoacidosis (DKA). Ensure glycemic control before initiation and maintain ongoing blood glucose monitoring to reduce the risk of this potentially fatal complication. We present a case of metastatic breast cancer with initially controlled blood glucose who developed ketoacidosis and myocardial infarction during capivasertib therapy.