A 62-year-old male smoker presents with weight loss and confusion. Serum corrected calcium is 12.6 mg/dL with normal serum PTH. CT shows a large central hilar mass, and biopsy reveals nests of cells with intercellular bridges and keratin pearls. The hypercalcemia is mediated by:

• A Ectopic secretion of parathyroid hormone itself
• B Calcitriol produced by tumor macrophages
• C Osteolytic bone metastases
• D PTH-related peptide secreted by the tumor ✓

Explanation

Keratin pearls and intercellular bridges identify squamous cell carcinoma, which is the lung cancer most classically linked to humoral hypercalcemia via secretion of PTH-related peptide. PTHrP mimics PTH action on bone and kidney but is not measured by standard intact PTH assays, explaining the suppressed native PTH. Ectopic true PTH production is vanishingly rare in lung cancer, and calcitriol-mediated hypercalcemia is the signature of 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.