Unusual Complication of a Pancreatic Neuroendocrine Tumor Presenting with Malignant Hypercalcemia

Context: Hypersecretion of PTHrP is a relatively common cause of malignancy-related hypercalcemia but has only been described in a few cases of neuroendocrine tumors (NET). Objective: The aim of this case report is to describe the clinical syndrome, complex therapeutic interventions, and unusual complications caused by persistent PTHrP hypersecretion in a patient with a pancreatic NET. Case Illustration: A 58-yr-old male patient presented with nonspecific abdominal pain and was found to have severe hypercalcemia secondary to a well-differentiated NET of the pancreas associated with extensive liver metastases. Elevated ionized calcium levels accompanied by low serum PTH and remarkably elevated PTHrP concentrations were consistent with PTHrP-related hypercalcemia that proved to be resistant to various chemotherapeutic regimens and supportive therapy. Partial control of the humoral syndrome was obtained only after the application of cytoreductive interventions and the introduction of various molecular targeted therapies. Due to persistent PTHrP action, bone disease emerged in the form of brown tumors. Discussion: The manifestation of paraneoplastic syndrome due to PTHrP hypersecretion, despite its rareness in NET, should be considered in the differential diagnosis of hypercalcemia in such tumors. Moreover, the appearance of bone lesions in this setting may be in the context of metabolic bone disease and could be misdiagnosed as bone metastases.