Non-invasive low-grade papillary urothelial carcinoma with whorled features: a report of two cases.

Non-invasive papillary urothelial carcinomas present as cytoarchitectural disorders without invasion through the basement membrane. They are divided into low-grade and high-grade categories on the basis of the extent of cytologic atypia and architectural disarray. Notably, divergent differentiation (such as squamous and glandular differentiation) and variants (such as nested, micropapillary, plasmacytoid, and sarcomatoid) are reported primarily in invasive and high-grade urothelial carcinomas. We present two cases of low-grade non-invasive papillary urothelial carcinoma with recently described whorled features (urothelial eddies). Both patients were 77-year-old males with small papillary lesions in the bladder. Histopathologic examination revealed low-grade non-invasive papillary urothelial carcinoma with a sporadic whorled pattern. Patient number 1's tumor exhibited cytokeratin (CK) 20 immunopositivity, up to 5% Ki-67 labeling, and wild-type p53 staining. Patient number 2's tumor was negative for CK20 with wild type p53 staining in portions with whorls, but demonstrated diffuse CK20 and extensive p53 staining (possible mutation) in tumor portions lacking whorls. Patient number 1 experienced a 14-month recurrence and a second possible recurrence 43 months after the initial diagnosis. Patient number 2 experienced recurrence of low-grade papillary urothelial carcinoma with focal whorls in one location and subsequently a distinct low-grade papillary urothelial carcinoma with whorled features in a different part of the bladder. Our limited study supports the reported association of rare whorled features with non-invasive low-grade papillary urothelial carcinoma, albeit with a diverse immunophenotype. Evaluation of both whorled and non-whorled areas in the histology along with CK20 and p53 staining may be helpful for complete diagnostic and prognostic evaluation of these cases.