A 62-year-old man with a 40 pack-year smoking history presents with weight loss and confusion. Serum calcium is 13.2 mg/dL with normal PTH. CT shows a cavitating mass in the left hilum. Biopsy shows nests of large polygonal cells with keratin pearls and intercellular bridges. The paraneoplastic mediator responsible for his hypercalcemia is:
- A Ectopic ADH secretion
- B PTH-related peptide secreted by the tumor ✓
- C Osteolytic bone metastases
- D Calcitriol produced by tumor-associated macrophages
Correct answer: B. PTH-related peptide secreted by the tumor
Explanation
The central location, cavitation, keratin pearls, and intercellular bridges identify squamous cell carcinoma, the lung cancer classically associated with humoral hypercalcemia via PTH-related peptide, which mimics PTH at bone and kidney but is not detected by standard PTH assays. Ectopic ADH causes hyponatremia, not hypercalcemia, and calcitriol-mediated hypercalcemia is a feature of sarcoidosis and lymphoma rather than squamous carcinoma.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.