Introduction: Capivasertib is a selective oral AKT inhibitor approved for hormone receptor-positive, HER2-negative advanced breast cancer with AKT pathway mutations. As AKT is integral to insulin signaling, its inhibition predisposes patients to hyperglycemia. We report a case of severe capivasertib-induced hyperglycemia with profound insulin resistance in a non-diabetic patient. Case: A 56-year-old female with metastatic breast cancer (ER/ PR-positive, HER2-negative, AKT1- and ESR1-mutated, TMB-high) presented with severe hyperglycemia following capivasertib initiation. She had no prior diabetes history, with a baseline hemoglobin A1c of 5.6%. Her first cycle (200 mg twice daily, 7 April 2025) was uncomplicated metabolically. The second cycle was escalated to 400 mg twice daily on 21 April 2025. By Day 3, blood glucose rose significantly. Premixed insulin 20 units failed to achieve glycemic control, necessitating intravenous insulin infusion. Despite escalation to 30 units per hour, euglycemia could not be achieved. Notably, there was no biochemical evidence of diabetic ketoacidosis or hyperosmolar hyperglycemic state, and the patient remained hemodynamically stable. No corticosteroids or other contributing medications were administered. Blood glucose normalized spontaneously approximately 36 hours after the last capivasertib dose, and all insulin was weaned and discontinued by 26 April 2025. She remained euglycemic without antidiabetic therapy thereafter. The patient and family opted for palliative care, and she passed away on 6 May 2025. Conclusion Capivasertib can precipitate severe, insulin-resistant hyperglycemia even in non-diabetic patients, without progression to overt hyperglycemic crisis. Spontaneous resolution upon drug cessation supports a direct drugmediated mechanism via AKT-disrupted insulin signaling. Clinicians should monitor glucose closely during therapy and consider drug cessation in refractory cases. Further studies are warranted to guide optimal glycemic management.
capivasertib ; Hyperglycemia ; Insulins