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.