Small cell carcinomas of the lung can ectopically secrete antidiuretic hormone (ADH) and adrenocoicotropic hormone (ACTH) or ACTH-like peptide to produce hyponatremia and Cushing syndrome, respectively. Ectopic production of hormones is one of the paraneoplastic syndromes that frequently can predate or accompany cancer. By definition, paraneoplastic syndromes must be independent of the direct effect of a rumor or its metastasis. Ceain tumors derived from non endocrine cells can ectopically produce hormones, examples of which include the small cell carcinoma of the lung producing ADH or ACTH or a primary squamous cancer of the lung producing a parathormone-like peptide. In the process of normal differentiation, there is suppression of some genes and activation of others. Carcinogenesis, however, often results in mutations that block the suppressor genes resulting in production of products that are not normally made by those cells. Renal adenocarcinomas have the potential for ectopically secreting parathormone-like peptide (hypercalcemia), gonadotropins (feminization or masculinization), renin (hypeension), and erythropoietin (secondary polycythemia). Hepatocellular carcinomas can ectopically secrete erythropoietin (secondary polycythemia) and an insulin-like peptide (hypoglycemia). Ref - Harrison's principles of internal medicine 20e pg 538,662