Malignant Hypercalcemia Induced by the Ectopic Production of Intact Parathyroid Hormone (PTH)

Malignant hypercalcemia is a common finding in patients with advanced cancer, involving mechanisms like tumor secretion of parathyroid hormone (PTH)-related protein, osteolytic metastases, and tumor production of calcitriol. Although rare, hypercalcemia induced by ectopic tumoral secretion of PTH can be an additional mechanism. Here we present an 84-year-old male patient who was admitted to the hospital with a non-productive cough, anorexia, and a single episode of small-volume hemoptysis. He was diagnosed with stage T4N3M1c left lung small cell carcinoma, and laboratory tests were remarkable for elevated ionized calcium as well as elevated serum intact PTH. A parathyroid 99mTc sestamibi scan showed no changes, suggesting ectopic production of PTH. Being a rare event, malignant hypercalcemia from intact PTH ectopic production should be considered in these patients.