The CAPItello-291 trial demonstrated that capivasertib combined with fulvestrant significantly prolonged progression-free survival in patients with hormone receptor–positive, HER2–negative advanced breast cancer, particularly in those with PIK3CA, AKT1, or PTEN mutations.1) However, frequent adverse events such as diarrhea, rash, and hyperglycemia have been reported, with hyperglycemia occasionally progressing to DKA. This evidence concerns the gene ERBB2 and breast cancer.