Low-grade micropapillary urothelial carcinoma: Does it exist? A SEER analysis of management and outcomes.

Abstract

315 Background: Micropapillary Urothelial Bladder Carcinoma (MPBC) is a rare aggressive variant histology of bladder cancer. Management of non-muscle invasive (NMI) MPBC is controversial, as bladder sparing strategies routinely used when managing TCC have resulted in worse outcomes. In order to better understand its behavior, we reviewed all MPBC pts in the SEER database and compared them with TCC pts. Methods: Data was collected from SEER 17. Age, sex, race, grade, stage, treatment, and cause of death were collected. Kaplan-Meier (KM) and Cox proportional hazards (CPH) models were performed. Results: From 2001-2008, 120 pts with MPBC were identified, 0.1% of all bladder cancer. Mean age was 70.3 yrs, 76.7% were male, and 90.8% were Caucasian. No difference in age, sex, or race was detected between MPBC and TCC pts. MPBC presented with more high grade (HG) disease (86.1% vs. 38.7%, p<0.0001) and with higher stage (40.8% NMI vs. 90.4% NMI, p < 0.0001). KM analysis demonstrated that NMI MPBC had significantly worse overall survival (OS) than NMI TCC (not controlling for grade, p<0.0001). Low grade (LG) NMI MPBC pts had worse OS and cancer specific survival (CSS) as compared to LG TCC pts (p=0.0037, p<0.0001 respectively), and did no better than HG NMI MPBC pts. No difference was detected between HG NMI MPBC and HG NMI TCC pts. A CPH model controlling for stage, grade, treatment, age, race, and sex detected no significant survival difference in MPBC vs. TCC (HR 1.04, p=0.7966). For NMI MPBC (n=49), only 4 pts underwent definitive therapy (2 had cystectomy and 2 received EBRT). During the median follow-up period of 31 months, no cancer specific deaths occurred in this group of pts. However, in those not receiving definitive therapy (n=45), 7 cancer specific deaths occurred (15.6%). Conclusions: MPBC is a rare variant with high stage and grade presentation. Controlling for stage and grade, no difference could be detected in survival between MPBC and TCC. However, LG NMI MPBC behaved similarly to both HG MPBC and HG TCC in regards to survival outcomes. We propose that all MPBC (regardless of grade) be managed as HG disease, and that strong consideration for definitive therapy should be given even in the setting of NMI disease.