Micropapillary urothelial carcinoma of the urinary bladder: a clinicopathological analysis of 72 cases

Aim: Micropapillary carcinoma (MPC) of the bladder is an aggressive variant of urothelial carcinoma (UC). It is unknown if any amount of a micropapillary component justifies the diagnosis of MPC. It is also unknown if surface MPC also has aggressive potential. Methods: We studied 72 patients with UC with a micropapillary component in transurethral resections of bladder (TURB) diagnosed between 1998 and 2008. Fifty-seven patients were treated with radical cystectomy. Tumours were classified according to pathological (pT) stage and percentage of MPC (<= 10%, 10-49%, 50-100%). This was correlated with clinical data and follow up. Significant factors in univariate analysis were entered into a multivariate analysis. Results: In the TURB specimens, 12 had pTa, 33 pT1 and 27 pT2 tumours with 23% also displaying urothelial carcinoma in situ (CIS). On cystectomy, the MPC component was upstaged in 79% of cases. Twenty-five (35%) patients had metastases at presentation or nodal metastases at cystectomy and 27 patients (38%) died of disease. Mean survival was 17.8 months. Of 12 pTa MPC cases, eight were treated with cystectomy, all displaying invasive carcinoma including five (62%) with pT2-pT4 disease. Three (25%) of these patients died of disease. Seven patients had a MPC component of <10% all of whom had cystectomy. Six of these had invasive carcinoma including two (33%) with pT2-pT4 disease. One (15%) of these patients died of disease. On univariate analysis, the proportion of the MPC component on TURB and pathological stage predicted disease specific survival (p=0.01 and 0.004, respectively), while presence of CIS predicted recurrence (p=0.03). On multivariate analysis, CIS predicted recurrence (p-0.003); however, the proportion of MPC in TURB did not remain significant in predicting disease specific survival. The pathological stage of MPC remained significant in predicting disease specific survival (p=0.04). Conclusions: Any amount of MPC, even <10% is significant in urothelial carcinoma and should be reported. Surface MPC is associated with invasive carcinoma in most cases which can be high stage. Adequate sampling to include detrusor muscle is crucial in these cases. Associated CIS is important to be recognised and reported as this also impacts on clinical outcome.