Urine cytology of micropapillary carcinoma of the urinary bladder.

A case of micropapillary carcinoma (MPC) of urinary bladder is presented, in which the urine smear was studied in detail in an attempt to better characterize the cytologic findings of MPC. When the voided urine was examined in low power, cancer cells were scattered in the specimens as compact papillary/spheroidal clusters composed of pleomorphic cancer cells. Solitary carcinoma cells were occasionally observed. High power view of the smear revealed that the papillae/spheroids consisted of high-grade urothelial carcinoma cells. The cancer cells had pleomorphic nuclei with coarsely granular chromatin and thickened, irregular nuclear membrane, and thick cytoplasm. Histologically, the tumor in the resected bladder appeared as small nests with surrounding hallo both in the luminal surface and in the site of wall involvement. These tightly bound papillary/spheroidal clusters comprised of highly atypical cancer cells were the most specific cytologic finding in the urine of MPC, which were considered as a key diagnostic clue of MPC. The background of the urine smear showed numerous granulocytes and bacilli compatible with cystitis, which is a previously known complication of MPC. Differential diagnoses of MPC from those with pertinent cytologic findings such as conventional UC (including glandular differentiation), and primary/secondary adenocarcinoma of urinary bladder are discussed with a brief review of literature.