The effect of tumor grade heterogeneity on recurrence in non-muscle invasive bladder cancer.

Abstract

To investigate the outcomes of mixed-grade non-muscle invasive bladder cancer (NMIBC) based on the degree of high-grade predominance. We identified patients in our institutional database who had a transurethral resection of bladder tumor(s) for NMIBC. Tumors with mixed-grade features on pathology report were reanalyzed, assigned the percentage high-grade component, and stratified into ≤ 5% high-grade and > 5% high-grade groups. All others were classified as low-grade or high-grade NMIBC. Differences in recurrence-free survival were assessed by log-rank test. A multivariable Cox regression model was used to evaluate the impact of tumor grade on recurrence, controlling for tumor stage, size, multifocality, and intravesical therapy. Two hundred and twenty patients were followed for a median of 2 years; 127 (58%) had low-grade NMIBC, 66 (30%) had high-grade NMIBC, and 27 (12%) had mixed-grade NMIBC. Of the mixed-grade patients, 14 had a ≤ 5% high-grade component, and 13 had a > 5% high-grade component. Recurrence rates across all groups ranged from 42% to 79%. There was no significant difference in intravesical recurrence-free survival among the grade categories as assessed by log-rank test. On multivariable Cox regression analysis, grade category was not significantly associated with likelihood of recurrence. The prognosis of mixed-grade histology in NMIBC has not previously been well defined. Although grade category was not found to be an independent significant predictor of recurrence, the recurrence rate for mixed-grade tumors was quite high overall. Further studies are required to better understand appropriate risk stratification and treatment of mixed-grade NMIBC.