RET/PTC1 is one of the most frequently found RET/PTC version and, in all the cases so far reported, it is invariably generated by the fusion of the first encoding exon of the H4 gene to the RET kinase encoding domain.     ///    "its transforming ability, however, is 5-fold lower than that of the classic RET/PTC1 isoform. "    ///     RET/PTC chimeric oncogenes are generated by the fusion of heterologous genes to the RET tyrosine kinase encoding domain. 