Invasive plasmacytoid urothelial carcinoma: A comparative study of E-cadherin and P120 catenin.

Invasive plasmacytoid urothelial carcinomas (PUCs) are an uncommon aggressive variant, which often shows immunohistochemical loss of E-cadherin, underlying its distinct discohesive histology. The marker P120 (well described in breast pathology as being a diagnostic tool alongside E-cadherin for lobular neoplasia) has not been evaluated in PUCs. Biopsies, transurethral resections, and cystectomies of PUCs were collected, and whole-slide immunohistochemical analysis of E-cadherin and P120 was applied. A subset of cases were also tested for CDH1 mutation. PUC cases were stratified into morphologic categories of classic, pleomorphic, or desmoplastic. For E-cadherin, 24 of 33 (73%) cases showed an abnormal staining pattern, consisting of complete absence of staining (17/24; 71%) or cytoplasmic staining (7/24; 29%). For P120, 24 of 33 (73%) cases showed an abnormal staining pattern, consisting of loss of membranous staining with cytoplasmic reactivity. Only 2 cases showed a discordant E-cadherin/P120 immunoprofile (94% concordance). Significant staining differences among the 3 morphologic categories were not found. CDH1 mutation was found in 4 of 8 (50%) of cases, with 3 of 4 (75%) cases showing matched molecular/immunoprofile reactivity. No cases with CDH1 mutation showed discordant pattern E-cadherin/P120 immunoreactivity. Our rate of aberrant E-cadherin immunoreactivity in PUCs (73%) is similar to a meta-analysis of published cases (74%). We also report an identical rate of aberrant P120 immunoreactivity in PUCs (73%). While PUC remains a histologic diagnosis, in a subset of cases showing a less appreciated pattern (such as desmoplastic) or confounding cytoplasmic E-cadherin reactivity, the utility of paired P120 staining may be a useful diagnostic tool.