Primary clear-cell urothelial carcinoma of urinary bladder: a not-so-clear entity with review of literature

Primary clear-cell urothelial carcinoma (CCUC) is an uncommon type of urothelial cancer with only 16 cases reported in published literature. Due to the rarity of the tumour, its clinical and prognostic values have not been clearly understood. We present one such rare clinical diagnosis in a 60-year- old man who underwent radical cystectomy (RC) with ileal conduit for urinary bladder cancer. Histopathology showed features of high-grade CCUC infiltrating the muscularis propria. Immunohistochemistry revealed diffuse immunopositivity of pan cytokeratin (CK), GATA3, P40, CK7 but was immunonegative for CD10 and vimentin. Our patient expired 4 months after diagnosis. CCUC has recently been included in the WHO 2016 classification of urothelial tumours. Most of the patients present with poor prognosis. Accurate diagnosis and recognition of this unusual variant are essential for better patient management and prognosis. Early RC seems to be the preferred way of management.

Clear Cell Urothelial Carcinoma

Clear cell urothelial carcinoma (CCUC) is a rare variant of urothelial carcinoma (UC) and its clinical significance has not been well elucidated. Consecutive cases of UC over a period of 5 years were reviewed. Histopathological tumor parameters, including the proportion of tumor cells with clear cell change, and patient outcomes were recorded. Expression of the following immunohistochemical markers was investigated: CK7, CK20, CK5, CD44, and PAX8. We also conducted a review of the literature for case reports/series of CCUC. Ten CCUCs were identified out of a total of 872 cases of UC. The clear cell component was characterized by prominent cytoplasmic membranes and voluminous clear cytoplasm, and accounted for 30% to 90% of the invasive tumor component. Of all the non-CCUC cases reviewed, at least 50% (noninvasive or invasive UC) showed focal areas of clear cell change that accounted for less than 5% of the neoplastic cells. Immunohistochemically, CCUC exhibited positive reactivity for CK5/CD44 (n = 9); CK20 (n = 5), PAX8 (very focal to extensive) (n = 6), and GATA3/CK7 (n = 10). Eight of 10 CCUC were of advanced clinical stage (pT3/pT4) and 6 of 10 experienced tumor recurrence and/or death due to disease. In conclusion, CCUC can be distinguished from non-CCUC by the extensive clear cell change in more than 30% of cells. This variant is associated with rapid progression to muscle invasion and metastasis, with an aggressive clinical course. Expression of CK5/CD44 may represent basal cell features in most CCUC cases, while PAX8 expression is suggestive of mesonephric derivation.