Clinicopathological characteristics and outcome of nested carcinoma of the urinary bladder

We present the clinicopathological features of 56 cases of the nested variant of urothelial bladder carcinoma. This is an uncommon variant of bladder cancer, recognized by the current WHO classification of urologic tumors. The nested component represented 100 % of the tumor in 24 cases. The architectural pattern of the tumor varied from solid expansile to infiltrative nests characterized by deceptively bland histologic features resembling von Brunn nests. Typical features of high-grade conventional urothelial carcinoma were present in 32 cases. Most neoplastic cells had nuclei of low to intermediate nuclear grade with occasional nuclear enlargement, most frequently seen in deep areas of tumor. The nested component expressed cytokeratins 7, 20, CAM5.2, and high molecular weight (34E12), p63, Ki67, p53, p27, and GATA3. Tumor extension was T1 (n = 9), minimally T2 (n = 10), T2a (n = 1), T2b (n = 4), T3a (n = 8), T3b (n = 13), and T4a (n = 11). On follow-up, 36 of patients died of or were alive with disease from 2 to 80 months (mean 21 months). Four patients died of other causes. Eleven other patients remained disease free. Univariate survival analysis showed no differences for nested carcinoma compared with conventional urothelial carcinoma. As in conventional urothelial carcinoma, in nested carcinoma of the bladder pT category defined different survival groups. In summary, nested variant of urothelial bladder carcinoma is typically associated with advanced stage. In samples of limited volume, it may be misdiagnosed as proliferation of von Brunn nests or other nested-like bladder lesions, delaying definitive therapy.