Paraneoplastic syndromes occur in 10% of patients with bronchogenic carcinoma. This review focuses on the three most common paraneoplastic syndromes: syndrome of inappropriate antidiuresis (SIAD), ectopic secretion of peptides of the proopiomelanocortin family (ectopic Cushing's syndrome), and hypercalcemia of malignancy.
Small cell lung carcinoma is the most common cause of SIAD and ectopic Cushing's syndromes. SIAD is characterized by hyponatremia, hypoosmolality, and less than a maximally diluted urine. Secretion of vasopressin by the tumor and inappropriate thirst are the causes of the syndrome. Treatment of the underlying malignancy, fluid restriction, and demeclocycline therapy are useful in the management of SIAD.
Ectopic Cushing's syndrome occurs in some carcinomas, mainly small cell lung cancer. The tumor produces adrenocorticotropin (ACTH) and its precursors resulting in hyperfunction of the adrenal cortex. Treating the carcinoma is the most important therapy. Ketoconazole, metyrapone, aminoglutethimide, and RU 486 are useful palliative treatments.
Hypercalcemia of malignancy is the most common cause of hypercalcemia in hospitalized patients. Squamous cell carcinoma is the histologic type most often associated with hypercalcemia. Humoral hypercalcemia, caused by tumor production of parathyroid-hormone-related protein, is the most common type of hypercalcemia of malignancy. The management of hypercalcemia in malignancy involves correcting the dehydration, enhancing renal excretion of calcium, inhibiting accelerated bone resorption, and treating the underlying malignancy.