FISH test (cytospin, original magnification Papanicolaou stain, 600×). Bladder washing 3 months after intravesical BCG treatment for pT1, HGUC. Atypical urothelial cells in a background of inflammation support the diagnosis of AUC. Nevertheless, morphology cannot distinguish between neoplastic cells and reactive cellular changes. Insert of the same atypical cell group, UroVysion FISH clearly shows a positive result with gain of the centromeric signals (blue, red, and green) and homozygous deletion of 9p21 (no yellow signals). Encircled is an inflammatory cell, which shows a regular disomic signal pattern and serves as internal negative control (original magnification, 600×).