Sangoi A, et al. - Urothelial carcinoma (nonglandular) in situ (CIS) have been reported to have 5 well-described morphologic patterns. Researchers here focused on a novel pattern of flat urothelial carcinoma with plasmacytoid features; this is marked by a triad of morphologic findings including abnormal architecture with cellular rounding, enlarged nuclei with eccentric nuclear localization, and dense globular eosinophilic cytoplasm. They reviewed the data of a total of 23 cases of plasmacytoid CIS (mean age: 74.1 y, range: 58 to 91 y). Based on the histologic features, the immunophenotype, the association with other forms of urothelial neoplasia, and the risk of recurrence and progression in de novo lesions, they suggest plasmacytoid CIS as a novel pattern of flat urothelial carcinoma. Relative to other more typical patterns of CIS, these histologic features may be more complex and hence should be carefully differentiated from therapy-related/reactive changes.