Severe Hypercalcemia as the Initial Presentation of a Neuroendocrine Carcinoma of Unknown Primary Site: A Case Report.

Hypercalcemia is a common paraneoplastic syndrome that is associated with many malignancies. Hypercalcemia develops in malignancies through various mechanisms. Parathyroid hormone-related protein (PTHrP) is secreted by malignancy involving the lungs, breast, colorectum, bladder, and, rarely, neuroendocrine tumors. This is a rare case of severe hypercalcemia as the initial presentation of a high-grade metastatic neuroendocrine tumor of an unknown primary site.