Whereas the prevalences of RET/PTC1 and RET/PTC3 were almost equal in classic and follicular PTC, all of the TCV-positive cases expressed the RET/PTC3 rearrangement.     ///    We have expressed the two oncogenes in PC Cl 3 rat thyroid epithelial cells and found that RET/PTC3 is endowed with a strikingly more potent mitogenic effect than RET/PTC1.     ///    RET/PTC1 and RET/PTC3 are the most prevalent variants.     ///    "Mechanistically, this difference correlated with an increased signaling activity of RET/PTC3. "    ///    These findings prompted us to compare RET/PTC3 and RET/PTC1 in an in vitro thyroid model system.     ///    Potent mitogenicity of the RET/PTC3 oncogene correlates with its prevalence in tall-cell variant of papillary thyroid carcinoma.. 