What is the most common paraneoplastic finding in lung cancer?

• A. Hyperuricemia
• B. Leukocytosis
• C. Hypercalcemia
• D. Hyperglycemia

Answer: (C)

Paraneoplastic syndromes in lung cancer come from tumor-secreted substances that mimic hormones. The most common of these is hypercalcemia caused by production of PTH-related peptide by squamous cell carcinoma of the lung. PTHrP acts like parathyroid hormone, stimulating osteoclasts to resorb bone and increasing renal calcium reabsorption, which raises serum calcium. Because PTHrP drives the rise, endogenous PTH is suppressed and vitamin D activation is not pathologically elevated, helping distinguish this mechanism.

This pattern aligns with the histology: squamous cell tumors are particularly associated with PTHrP-mediated hypercalcemia, whereas small cell carcinomas more often cause ectopic hormone syndromes like SIADH (low sodium) or ectopic ACTH production (Cushing syndrome). Other options like hyperuricemia, leukocytosis, or hyperglycemia are not the classic paraneoplastic signatures of lung cancer.