We report a patient with hyperthyroidism due to a FTC bearing an activating TSHR mutation and PAX8-PPARgamma rearrangements.     ///    Identification of a paired box gene 8-peroxisome proliferator-activated receptor gamma (PAX8-PPARgamma) rearrangement mosaicism in a patient with an autonomous functioning follicular thyroid carcinoma bearing an activating mutation in the TSH receptor..     ///     Our main objective was to search for mutations in candidate genes and for paired box gene 8-peroxisome proliferator-activated receptor gamma (PAX8-PPARgamma) rearrangement in a well-differentiated angioinvasive follicular thyroid carcinoma (FTC) causing hyperthyroidism.     ///    "under complete medium conditions, co-transfection of PAX8-PPARgamma with either TSHR-M453T or TSHR-WT inhibited cell proliferation. "    ///    "We searched for PAX8-PPARgamma in thyroid, PBL, and uterine leiomyoma samples from the patient and family members. "    ///    PAX8-PPARgamma was present as a mosaicism affecting tissues from endodermal and mesodermal origin.     ///    "Under deprived medium condition, co-transfection of PAX8-PPARgamma and TSHR-M453T dramatically increased the number of thyrocytes, an effect that it was not observed with TSHR wild-type (WT). "    ///    PAX8-PPARgamma and TSHR-M453T inhibited or promoted thyrocyte proliferation depending on medium conditions. 