Nested variant of urothelial carcinoma of urinary bladder strongly expressing NSE, KIT and PDGFRA

Abstract

The nested variant of urothelial carcinoma (NVUC) of urinary bladder (UB) is very rare and is characterized by the presence of benign-appearing urothelial carcinoma cells in lamina propria, sparing surface urothelial involvement. It shows aggressive clinical course despite the benign-looking histology. A 72-year-old woman presented with dysuria. Cystscopy revealed papillary infiltrative tumor, and transurethral resection of UB tumor (TUR-BT) was performed. It was composed of small three fragments, two of which showed urothelial carcinoma (UC) of low grade (G1) atypia. In one section, NVUC was seen. The nested areas showed small clusters of UC of mild atypia. They were remote from surface urothelium. The tumor was mildly invasive, and the pathological stage was pT1. Immunohistochemically, tumor cells were positive for various types of cytokeratins, EMA, p63, p53, MUC1, NSE, KIT, PDGFRA, Ki-67 (43%), NCAM and synaptophysin. This is the first case of NVUC of UV with neuroendocrine features and expressions of KIT and PDGFRA.