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

Abstract

Objective: To investigate the outcomes of mixed-grade non-muscle invasive bladder cancer (NMIBC) based on the degree of high-grade predominance.

Methods: 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.

Results: 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.

Conclusions: 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.

Keywords: Non-muscle invasive bladder cancer; mixed-grade.