A 68-year-old heavy smoker presents with weight loss and a serum calcium of 13.4 mg/dL with suppressed intact PTH. CT shows a centrally located right hilar mass invading the bronchus. Biopsy shows keratin pearls and intercellular bridges. The hypercalcemia is mediated by which substance?
- A Parathyroid hormone related protein produced by the tumor ✓
- B Ectopic secretion of ACTH
- C Antibodies against voltage-gated calcium channels
- D 1-alpha hydroxylase activity within tumor tissue
Correct answer: A. Parathyroid hormone related protein produced by the tumor
Explanation
Squamous cell carcinoma is typically central, arises from bronchial epithelium, and is the subtype classically linked to hypercalcemia of malignancy via secretion of PTHrP, which mimics PTH at bone and kidney but suppresses native PTH by feedback. Ectopic ACTH and anti-voltage-gated calcium channel antibodies are features of small cell carcinoma, while ectopic calcitriol occurs mainly in lymphoma.
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.