Plasmacytoid/diffuse urothelial carcinoma: a single-institution immunohistochemical and molecular study of 69 patients.

Accurate diagnosis of plasmacytoid urothelial carcinoma (PUC) is important given its poor prognosis and frequent presentation at high stage. We aim to assess the clinicopathological features, molecular aberrations, and follow-up data in a series of PUC cases from a single tertiary cancer center. Seventy-two urinary bladder, ureteral, and renal pelvic specimens with urothelial carcinoma with plasmacytoid differentiation were identified. Immunohistochemical stains were performed on 48 cases. Among urinary bladder origin markers, GATA3 was most sensitive (96%). Breast carcinoma markers (estrogen receptor, mammaglobin) were usually negative, but progesterone receptor stained 1 case (4%). Neuroendocrine markers CD56 and TTF-1 were each positive in 1 case (4% and 4%, respectively). Gastrointestinal adenocarcinoma marker CDX2 was positive in 4 cases (15%), but nuclear β-catenin was negative in all cases. CD138 was positive in 83% and E-cadherin expression was lost in 57% of cases. Fluorescence in situ hybridization using the UroVysion Bladder Cancer Kit and FGFR3 mutational analysis using polymerase chain reaction were performed on 15 cases; deletion of chromosome 9p21 was common (60%), and FGFR3 mutations were detected in 60% of cases (5 cases had both deletion 9p21 and FGFR3 mutations). Cases were divided into 3 morphologic groups: classic (29%), desmoplastic (35%), and pleomorphic (36%). The 3 morphologic subtypes had distinct survival outcomes (P = .083), with median survival for all patients 18 being months versus 10 months for the desmoplastic group.