A 58-year-old man with squamous cell carcinoma of the lung develops hypercalcemia (serum calcium 13.2 mg/dL) without bone metastases. The most likely mediator responsible for this paraneoplastic hypercalcemia is:

• A Ectopic parathyroid hormone (PTH)
• B 1,25-dihydroxyvitamin D (calcitriol)
• C Prostaglandin E2
• D Parathyroid hormone-related protein (PTHrP) ✓

Explanation

Squamous cell carcinoma of the lung is the classic cause of humoral hypercalcemia of malignancy, mediated by PTHrP secreted by the tumor. PTHrP binds PTH receptors in bone and kidney, mimicking PTH action but unlike PTH, PTH levels are suppressed. True ectopic PTH secretion is vanishingly rare; calcitriol-mediated hypercalcemia is seen in lymphomas.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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