The prevalence of RET/PTC1, RET/PTC2, and RET/PTC3 has been found to vary between 0% and 20% in most series of sporadic (nonradiation-induced) PTCs analyzed by type-specific reverse transcription-polymerase chain reaction (RT-PCR) alone.     ///    "In our study, RET/PTC1, RET/PTC2, and RET/PTC3 oncogenes were found in only 7 of 105 (7%) sporadic PTCs. "    ///    "RT-PCR was also performed with two different primer sets for RET/PTC1, RET/PTC2, and RET/PTC3 followed by Southern hybridization in the first 62 tumors. "    ///    "Of these tumors, 3 involved RET/PTC1 and 4 involved RET/PTC3. "    ///    "RT-PCR was performed to amplify fusion products of RET/PTC1, RET/PTC2, RET/PTC3, and ELKS-RET from frozen tissue of 105 sporadic PTCs. "    ///    "Because the high prevalence of RET rearrangements in Chinese patients was particularly striking, we were prompted to reexamine chimeric transcripts of RET/PTC1, RET/PTC2, and RET/PTC3 using the same experimental designs in a larger number of cases in the same population. "