Tumor mutational burden (TMB) and BCG responsiveness in high-risk non-muscle invasive bladder cancer (NMIBC).

Abstract

442 Background: Despite optimal management of NMIBC with transurethral resection of bladder tumor (TURBT) and intravesical BCG therapy, a significant proportion of patients (pts) will eventually present with disease recurrence or progression. To date, there is no validated predictive biomarker to guide patient selection for the most appropriate therapy in this setting. Methods: We retrospectively identified pts with high-risk NMIBC treated with TURBT, repeat TUR and intravesical BCG (≥ 6 instillations) from 2009 to 2016. Patients were classified as BCG-responsive (BCG-R) and BCG-unresponsive (BCG-UR) based on the International Bladder Cancer Group criteria. Whole exome sequencing was performed using archival FFPE tumor tissue from pre-BCG TURBT samples. Association of genomic variables and outcomes was evaluated by Cox proportional hazards survival analysis and likelihood ratio tests. Results: Thirty-five patients were included (BCG-R = 17, BCG-UR = 18). Median follow-up was 46 months for BCG-R and 52 months for BCG-UR pts. The majority of pts was male (91.4%), former smoker (60%), and presented with high-grade urothelial carcinoma (85.7%) and/or T1 staging (71.4%). Median time for relapse and progression was 10.5 and 19 months, respectively, in the BCG-UR group. In this cohort, TMB was significantly different in BCG-R and BCG-UR groups, with a median TMB of 5.53 +- 4.60 and 3.17 +- 1.82 mutations/Mb, respectively ( P= 0.045). TMB was also associated with relapse-free survival (RFS), with a median RFS of 38 and 15 months in high versus low TMB groups, respectively ( P= 0.0092). Intratumoral genetic heterogeneity assessed by mutant-allele tumor heterogeneity (MATH) was not statistically different between the groups, with a median MATH score of 31.8 and 21.9 for BCG-R and BCG-UR ( P= 0.14), respectively. On multivariate analysis, age and TMB were independently associated with RFS. Conclusions: In this exploratory biomarker study, high TMB was associated with benefit from immunotherapy with BCG for NMIBC. The identification of predictive biomarkers in this setting is an important unmet need and integrative analysis of TMB with other potential predictive biomarkers should be assessed in larger datasets.