Low stage/grade tumors are often characterized by mutations in fibroblast growth factor receptor 3 (FGFR3)[5, 6] and rat sarcoma (RAS) genes [5, 7], while flat carcinoma in situ lesions frequently show mutations in TP53 in addition to a loss of heterozygosity of the retinoblastoma (RB) gene [3, 5, 8, 9]. Here, FGFR3 is linked to in situ carcinoma.