Acute Pancreatitis as the Initial Presentation of Metastatic Breast Cancer Due to Malignant Hypercalcemia: A Case Report.

Hypercalcemia-induced acute pancreatitis is a rare condition, most commonly associated with primary hyperparathyroidism or advanced malignancies, and represents a metabolic emergency. We report the case of a 63-year-old woman who presented with severe epigastric abdominal pain, constipation, and episodes of disorientation. Laboratory tests revealed elevated pancreatic enzymes and severe hypercalcemia. Acute pancreatitis secondary to hypercalcemia was diagnosed, and normal parathyroid hormone (PTH) levels excluded primary hyperparathyroidism. The presence of anemia, thrombocytopenia, and multiple lytic bone lesions initially suggested multiple myeloma; however, this diagnosis was ruled out due to the absence of monoclonal gammopathy. Further imaging revealed an irregular right breast mass with axillary lymphadenopathy, classified as BI-RADS 5. Tumor markers were markedly elevated, and core needle biopsy confirmed human epidermal growth factor receptor 2 (HER2)-positive invasive ductal carcinoma with bone metastases. Despite intensive treatment with intravenous hydration and zoledronic acid, neurological deterioration occurred; hence, after 25 days of hospitalization, the patient was discharged for home-based palliative care at the family's request. This case highlights the importance of considering metastatic malignancies, particularly breast cancer, in patients with pancreatitis of unclear etiology and severe hypercalcemia.