A 58-year-old man with squamous cell carcinoma of the lung develops hypercalcemia despite the absence of bone metastases. Serum PTH is undetectable. Which molecule secreted by the tumor is most directly responsible?
- A Parathyroid hormone-related protein (PTHrP) ✓
- B Calcitonin
- C 1,25-dihydroxyvitamin D
- D Osteocalcin
Correct answer: A. Parathyroid hormone-related protein (PTHrP)
Explanation
Humoral hypercalcemia of malignancy is most commonly mediated by PTHrP, which binds PTH receptors on bone and kidney, mimicking PTH action while native PTH is suppressed. Squamous cell carcinomas of the lung are the classic producers. Calcitonin lowers calcium; 1,25-dihydroxyvitamin D excess is seen in lymphomas, not squamous cell carcinoma; osteocalcin is a bone matrix protein.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.