These lesions occur in almost 50% of papillary cancers and consist in the juxtaposition of the 3' tyrosine kinase domain of the RET gene which codes for a receptor protein not normally expressed in follicular cells with the 5' domain of ubiquitously expressed genes, giving rise to several types of RET/PTC, papillary thyroid carcinomas, chimeric genes. Here, RET is linked to differentiated thyroid carcinoma.