RET and medullary thyroid gland carcinoma: Briefly, in 25% of MTC cases, the disease is hereditary, occurring as part of the MEN 2 syndromes (MEN 2A, MEN 2B, and familial medullary thyroid cancer) due to germline activating mutations of theRET receptor tyrosine kinase gene.RET is also mutated in about 50% of sporadic cases of MTC; in both hereditary and sporadic cases, specific mutations are correlated with phenotype and prognosis4,6.