Frameshift mutations (Fsindel) complement tumor mutation burden (TMB) in predicting survival after immune checkpoint inhibitors (ICI) in a pancancer analysis.

Abstract

2617 Background: ICI benefit certain patients (pts) with various malignancies and discovering biomarkers for response is an active research field. Recently, higher TMB (top 20% in each histology) based on nonsynonymous single nucleotide variants from MSK-IMPACT was shown to correlate with superior survival in a pancancer cohort. Fsindels may generate more immunogenic neoantigens and robust T cell infiltrates, thus predicting better responses to ICI. We previously demonstrated the clinical implication of fsindel in lung cancer pts on ICI. However, its value in other solid cancers has not been evaluated. Methods: Comprehensive genomic profiling (CGP) of the tumors was performed by FoundationOne to derive fsindel and TMB as previously described. Pts with advanced solid cancers who received ICI and had CGP available were included. We categorized pts into two groups; 0 fsindel (FS-) and more than 1 fsindel (FS+). Also, they were categorized into TMB high (top 20%) and TMB low (bottom 80%) within their own histology. Progression free survival (PFS) and overall survival (OS) were compared. Results: One hundred thirty-one pts excluding lung cancer were included. There were 11 histology groups: 14 soft tissue sarcomas, 19 GU, 23 GI, 23 skin, 10 HEENT, 10 RCC, 9 GYO, 6 pancreas, 5 mucosal melanoma, 4 breast, and 8 others. 74 pts received pembrolizumab, 25 nivolumab, 29 ipilimumab/nivolumab, and 3 atezolizumab. All pts had metastatic disease, mean age was 61 years and 55 (42%) were women. Among the 131 pts, 74 were FS- and 57 FS+. The presence of fsindel (FS+) was significantly correlated with overall response (p = 0.032) and clinical benefit rates (p = 0.025). TMB-high did not show any significant difference in PFS (p = 0.1) or OS (p = 0.28) when compared to the TMB low. However, in a combined model of TMB and fsindel, TMB high and FS+ patients had significantly better PFS compared to patients who had either TMB high or FS+ or neither (TMB low and FS-) (p = 0.021). Conclusions: Combined model of TMB high and fsindel (+) correlated with superior PFS in advanced solid cancer pts on ICI, in concordance with previous report for lung cancer. Validation in a larger cohort is underway.