The ligand-independent activation of RET is caused by gain-of-function mutations manifesting clinically as MEN2 or the formation of a fusion protein containing the intracellular kinase domain of RET and N-terminal domain from another protein with the ability to dimerize, resulting in the development of papillary thyroid carcinoma (PTC) [102,105]. The gene discussed is RET; the disease is thyroid gland papillary carcinoma.