Bertz S, Ensser A, Stoehr R,, et al. - This study was undertaken to present variant morphology and random chromosomal integration of BK polyomavirus in posttransplant urothelial carcinomas. Researchers conducted immunohistochemistry (IHC) screening for polyomavirus large T antigen (LTag) in 94 micropapillary urothelial carcinoma (MPUC), 480 unselected UC, 199 muscle invasive UC (including 83 UC with variant differentiation), 76 cases of plasmocytoid, nested and large nested UC and 15 posttransplant UC. In this study, LTag expressing UC was detected which were diagnosed between 2 and 18 years after kidney (n = 4) or heart (n = 1) transplantation. The outcomes of this study demonstrated that LTag expression of integrated BKPyV genomes and resulting p53 inactivation lead to aggressive high-grade UC with unusual, often micropapillary morphology.