Microcystic urothelial carcinoma: morphology, immunohistochemistry and clinical behaviour

To report on the clinicopathological features of 20 cases of microcystic urothelial bladder carcinoma.

The extent of microcystic component varied from 50-100% of the specimens. The cysts were round-oval and of varying sizes; the periphery of large cysts was frequently punctuated by many smaller cysts. The cysts were lined by urothelial, low columnar cells or by a single layer of flattened epithelium of low-intermediate nuclear grade. Focal high-grade conventional urothelial carcinoma was present in eight cases. Immunohistochemistry demonstrated variable positivity for cytokeratins 7 and 20, MUC1, MUC5AC, p63 and GATA3. Extent of expression of Ki67, p53 and p27(kip1) ranged from 20-60%, 10-40% and 10-30% of cells, respectively. On follow-up, 11 patients died of disease at 11-56 months and three patients were alive with disease at 26-37 months. Univariate survival analysis showed no differences for microcystic carcinoma versus conventional urothelial carcinoma (P = 0.548).

Microcystic urothelial carcinoma may pose diagnostic difficulties, especially in limited biopsy samples, where it may be mistaken for cystitis glandularis or adenocarcinoma of the bladder. Histological features, clinical history and appropriate immunohistochemical studies should help to distinguish it from its mimics. Aggressiveness seems to be related to higher stage at diagnosis.