A subset of the follicular variant of papillary thyroid carcinoma harbors the PAX8-PPARgamma translocation

The occurrence of the PAX8-PPARgamma fusion gene is thought to be restricted to follicular tumors (adenomas and carcinomas) of the thyroid (FTA and FTC). Using interphase fluorescent in situ hybridization (FISH), together with recombinant tissue-type polymerase chain reaction (RT-PCR) and immunohistochemistry, we detected the PAX8-PPARgamma translocation in 4 of 8 cases of the follicular variant of papillary thyroid carcinoma (FVPTC) exclusively or almost exclusively (>95%) composed of follicles. The 4 tumors with the translocation were larger and apparently more invasive than the remaining tumors, but the series is too small to allow a statistically meaningful comparison of the data. Our findings show that follicular thyroid carcinoma (PTC) may also harbor the PAX8-PPARgamma fusion gene and indicate that a subset of FVPTC shares some molecular features of FTA and FTC.