Is thyroid follicular cancer in Japanese caused by a specific t(2; 3)(q13; p25) translocation generating Pax8-PPARγ fusion mRNA?

A recent western study reports that t(2; 3)(q13; p25) translocation resulting in the expression of the Pax8-PPARγ fusion gene in patients with thyroid follicular carcinoma (FTC) occurs with high incidence (63%). Furthermore, the products of the fusion gene were shown to suppress the function of PPARγ in a predominantly negative manner, conferring them with an oncogenic potential. We examined the expression of this fusion gene in FTC in Japanese patients. From 1989 to 2000, six cases with FTC were surgically treated at our institute. In these carcinoma samples, the expression of mRNAs for the Pax8-PPARγ fusion product was analyzed by nested RT-PCR. Their expression was also studied in other thyroid nodules (12 adenomatous goiters, 12 follicular adenomas, 12 papillary carcinomas and 12 normal thyroid tissues) obtained at surgery during the same period. Pax8-PPARγ fusion mRNA was not detected in any FTC samples nor in the other samples. Furthermore, none of the 6 FTCs, one follicular adenoma or one normal thyroid analyzed by fluorescence in situ hybridization (FISH) exhibited Pax8-PPARγ gene fusion. These findings are in contrast to previous reports and indicate that ethnic background may affect the translocation.