RET and neoplasm: Germline gain-of-function mutations of the rearranged during transfection (RET) proto-oncogene, mostly occurring in exons 8, 10, 11, 13, 14, 15 and 16, activate RET via autophosphorylation of the transmembrane receptor tyrosine kinase; these mutant receptors are highly expressed in MEN2-related tissues, leading to tumour growth.