Low frequency of rearrangement of TRK protooncogene in Chinese thyroid tumors.

The TRK protooncogene (NTRK1) encodes a cell-surface transmembrane tyrosine kinase (TK) acting as a receptor for nerve growth factor. Oncogenic potential in thyrocytes results from replacing the 5' portion by regulatory parts of other genes, leading to constitutive TK expression. In Italy, human papillary thyroid carcinoma (PTC) shows a frequent activation (50%) of the TK receptor genes NTRK1 and RET. Both genes undergo oncogenic rearrangements by the same mechanism. We previously reported high frequency (6/11) of rearrangement of the RET protooncogene in Chinese PTCs. Wide differences in the frequency (0-10.9%) of the NTRK1 rearrangement in PTCs have been reported in different populations. To investigate the frequency of TRK protooncogene rearrangement in Chinese thyroid tumors, we performed reverse transcriptase polymerase chain reaction to amplify specific TRK rearrangement transcripts. We examined thyroid tumors of 40 patients, including 14 papillary carcinomas, 4 follicular carcinomas, 1 Hurthle cell carcinoma, 1 insular carcinoma, and 20 nodular goiters. NF874 NIH3T3, NF723 NIH3T3, NF861 NIH3T3, and NF881 NIH3T3 were used as controls for TRK-T3, TRK-T2, TRK-T1, and TRK, respectively. No known TRK protooncogene rearrangements were detected among the 40 thyroid tumors in our studies. We suggest that the TK receptor NTRK1 activation seems less important than RET activation in PTCs in the Chinese population.