Low Frequency of Rearrangements of the ret and trk Proto‐oncogenes in Japanese Thyroid Papillary Carcinomas

We investigated the frequency of rearrangements of the ret and trk proto‐oncogenes in Japanese thyroid tumors. DNAs from 38 thyroid papillary carcinomas and 14 follicular adenomas were analyzed by Southern blotting. Rearrangements of the ret and trk proto‐oncogenes were detected in one and two papillary carcinomas, respectively, but not in follicular adenomas. Analysis by a reverse transcriptase‐polymerase chain reaction method showed that the ret rearrangement‐positive tumor contained the PTC/ref^TPCchimeric transcript, which was reported to be found specifically in thyroid tumors and adenomatous goiter. We also found that rearranged mRNA of the trk proto‐oncogene was expressed at high levels in one of two trk rearrangement‐positive tumors. Our results indicated that the frequency of rearrangements of these proto‐oncogenes in Japanese papillary carcinomas was much lower than that in Italian patients.