RET and multiple endocrine neoplasia: About 25% of MTCs are familial (fMTC) and are described as multiple endocrine neoplasia syndromes: MEN2A (associated with pheochromocytoma and/or hyperparathyroidism), MEN2B (associated with marfanoid features and occasionally pheochromocytoma) and FMTC (familial medullary thyroid carcinoma only) which represents a variant along the spectrum of disease expression in MEN2A (1).