The fusion event corresponding to the rearrangement reciprocal to that leading to the formation of RET/PTC3 was also identified and characterized.     ///    "This previously uncharacterized gene is fused with the tyrosine kinase (tk) domain of the RET proto-oncogene to generate the oncogenic sequence RET/PTC3, thus providing a third example of RET oncogenic activation in papillary thyroid carcinomas. "    ///    The karyotype of two RET/PTC3 positive tumors did not show any evidence of chromosome 10 abnormalities.     ///    The two genes generating RET/PTC3 are localized in chromosomal band 10q11.2..     ///    The data indicate that a cytogenetically undetectable paracentric inversion within 10q11.2 generates RET/PTC3.. 