Which paraneoplastic syndrome is most commonly associated with small cell carcinoma of the lung?

Which paraneoplastic syndrome is most commonly associated with small cell carcinoma of the lung?

• A. Hypercalcemia due to PTHrP
• B. SIADH
• C. Lambert-Eaton syndrome
• D. Cushing syndrome

Answer: (B)

Small cell lung cancer often secretes hormones outside normal control, and the most common paraneoplastic effect is SIADH from ectopic ADH production. This leads to water retention and dilutional hyponatremia, with low serum osmolality and inappropriately concentrated urine, typically in a euvolemic patient. Clinically this can cause confusion, weakness, or seizures as sodium falls. Other paraneoplastic effects can occur with small cell cancer, such as Lambert-Eaton syndrome or, less commonly, ectopic ACTH causing Cushing syndrome, but SIADH is the hallmark and most frequent association. Hypercalcemia due to PTH-related peptide is more characteristic of squamous cell lung cancer, not small cell.

Small cell lung cancer often secretes hormones outside normal control, and the most common paraneoplastic effect is SIADH from ectopic ADH production. This leads to water retention and dilutional hyponatremia, with low serum osmolality and inappropriately concentrated urine, typically in a euvolemic patient. Clinically this can cause confusion, weakness, or seizures as sodium falls. Other paraneoplastic effects can occur with small cell cancer, such as Lambert-Eaton syndrome or, less commonly, ectopic ACTH causing Cushing syndrome, but SIADH is the hallmark and most frequent association. Hypercalcemia due to PTH-related peptide is more characteristic of squamous cell lung cancer, not small cell.