Diagnose carcinoid syndrome. The classical syndrome includes flushing and vasomotor instability, diarrhea, hepatomegaly, and endocardial lesions. Ectopic production may occur from oat cell carcinomas of lung, islet cell tumors of pancreas, and medullary carcinoma of the thyroid. Carcinoid tumors occur in multiple endocrine neoplasia, types I or II.