The aim of this study was to test whether the proximity effects that are observed between loci involved in RET/PTC rearrangements in humans are conserved across different species.     ///    "Using 3D fixation, fluorescence in situ hybridization, and confocal microscopy, we compared the distance between genes involved in RET/PTC rearrangement in normal thyroid cells from humans, mice, and rats. "    ///    The differences in nuclear architecture and spatial positioning of genes involved in RET/PTC rearrangements between human and rodent thyroid cells raise a concern about suitability of animal models for assessing RET/PTC-driven thyroid carcinogenesis in humans..     ///    "Recently, nuclear architecture and spatial proximity between recombinogenic genes have been implicated as important factors in the generation of RET/PTC and other chromosomal rearrangements in human cells. "    ///    RET/PTC is a characteristic genetic alteration frequently found in radiation-induced thyroid cancer in human populations.     ///    "We further observed that in human thyroid cells, mean distance between genes involved in two most common types of RET/PTC, that is, RET and NCOA4 (partners of RET/PTC3) and RET and H4 (partners of RET/PTC1), was 1.08??0.04 and 1.24??0.05??m, respectively. "