What happened, in summary

A 72-year-old woman with metastatic breast cancer had completed seven cycles of capecitabine over seven months when she developed a week of malaise, nausea, poor appetite, intense thirst, frequent urination, and dehydration. Her blood glucose was approximately 40 mmol/L, serum osmolality was 362 mmol/kg, and HbA1c had risen from 6.3% before capecitabine to 8.8%. She was diagnosed with hyperosmolar hyperglycemic state. She received intravenous fluids and insulin, then transitioned to a basal-bolus insulin regimen before discharge. Capecitabine was suspended while her oncology team reviewed the treatment. A CT scan during hospitalization showed reduction of her known metastatic lesions and no pancreatic lesion, supporting a drug-related metabolic complication rather than progression involving the pancreas. After discharge, her family doctor and diabetes team followed her closely. Subsequent capecitabine cycles remained on hold. Her glucose control improved enough to stop short-acting insulin and reduce glargine to 10 units daily. The cancer had shown radiographic improvement on capecitabine, but the severe hyperglycemic complication required treatment interruption and ongoing diabetes management.