Calcitriol-Mediated Hypercalcemia Due to Liver Metastases in a Patient With Primary Pancreatic Neuroendocrine Tumor

Hypercalcemia is most commonly associated with primary hyperparathyroidism or malignancy in the setting of elevated parathyroid hormone-related protein or bone metastases. Calcitriol (1,25-dihydroxyvitamin D)-mediated hypercalcemia is rare and typically associated with granulomatous conditions; however, other solid-organ etiologies have been reported. Here, we detail the case of a 62-year-old man with metastatic pancreatic neuroendocrine tumor (pNET) with hypercalcemia refractory to traditional bisphosphonate therapy in the setting of vastly elevated 1,25-dihydroxyvitamin D. Only after initiation of chemotherapy with capecitabine and temozolomide did his serum calcium consistently improve and 1,25-dihydroxyvitamin D begin to decrease. There are fewer than 5 reported cases of a pNET resulting in calcitriol-mediated hypercalcemia. Prompt initiation of treatment for the underlying condition can result in a significant improvement in serum calcium or 1,25-dihydroxyvitamin D. Multiple reports have also demonstrated success with high-dose steroid administration in patients with other solid-organ etiologies of calcitriol-mediated hypercalcemia, but this has not yet been reviewed in the pNET population.