A 55-year-old man with squamous cell carcinoma of the lung develops hypercalcemia (serum calcium 13.2 mg/dL) with a suppressed PTH. Which mediator is MOST responsible for this paraneoplastic hypercalcemia?
- A PTHrP (parathyroid hormone-related protein) ✓
- B Interleukin-6
- C Ectopic calcitriol (1,25-dihydroxyvitamin D)
- D Prostaglandin E2
Correct answer: A. PTHrP (parathyroid hormone-related protein)
Explanation
PTHrP is the dominant mediator of humoral hypercalcemia of malignancy in solid tumors, particularly squamous cell carcinoma of the lung, head, neck, and renal cell carcinoma. It binds the PTH receptor, stimulating osteoclastic bone resorption and renal calcium reabsorption, but suppresses native PTH via feedback. Ectopic calcitriol is the mechanism in lymphoma-associated hypercalcemia, not squamous carcinoma.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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