RET (rearranged during transfection proto-oncogene) encodes a tyrosine kinase (TK) receptor. Translocations involving RET were first described in Papillary Thyroid Carcinoma (PTC) where somatic rearrangements result in the fusion of its TK catalytic domain with an N-terminal dimerization domain encoded by various fusion partner genes. RET rearrangements occur in approximately 1-2% of Lung Adenocarcinomas and 10-20% of Papillary Thyroid Carcinomas. Detection of RET rearrangements is useful for diagnostic classification of disease and for predicting tumor response to targeted therapy.