Evidence for a 3p25 breakpoint hot spot region in thyroid tumors of follicular origin

Epithelial tumors of the thyroid are cytogenetically well-investigated tumors. So far, the main cytogenetic subgroups, characterized by trisomy 7 and by rearrangements of either 19q13 or 2p21, respectively, have been described. Recently, we have been able to describe the involvement of a novel gene called THADA in benign thyroid lesions with 2p21 rearrangements. Other fusion genes found in thyroid lesions are RET/PTC and PAX8/PPAR gamma. The latter occurs in follicular thyroid carcinomas with a t(2;3)(q13;p25). Here we present molecular-cytogenetic and cytogenetic investigations on a follicular thyroid adenoma with a t(2;20;3)(p21;q11.2; p25). In this case, an intronic sequence of PPAR gamma is fused to exon 28 of THADA. We used BAC clones containing the genomic sequence of PPAR gamma for fluorescence in situ hybridization to confirm the localization of the breakpoint within intron 2 of PPAR gamma. Our findings suggest that the close surrounding of PPAR is a breakpoint hot spot region, leading to recurrent alterations of this gene in thyroid tumors of follicular origin including carcinomas as well as adenomas with or without involvement of PAX8.