Acute hyperglycemic hyperosmolar syndrome associated with capivasertib, a new, oral targeted therapy for advanced breast cancer.

Capivasertib is a new targeted therapy for the treatment of select cases of hormone receptor positive, HER2 negative advanced breast cancer. Hyperglycemia is a known adverse effect of capivasertib with a 16 % incidence rate, however life-threatening hyperglycemia occurs rarely (incidence 0.3 %). We describe a case of severe hyperglycemic hyperosmolar syndrome with serum blood glucose of 1558 mg/dL in an 86 year old female patient presenting to the emergency department 16 days after starting oral capivasertib. Capivasertib was held on admission, and the patient received three days of insulin infusion therapy before transitioning to mealtime insulin coverage without need for basal coverage. Her initial presentation was complicated by altered mental status, hypothermia, hypotension, and bradycardia, and she required over a week of intensive care. This case highlights the need for awareness of acute, severe hyperglycemia as a potential adverse effect of capivasertib and similar oncologic agents. Clinicians should ensure at least twice weekly blood glucose monitoring for any degree of capivasertib-induced hyperglycemia, and have high suspicion for this contributing factor in cases of severe hyperglycemia.