Real-world data evaluating immunotherapy markers and checkpoint inhibitor response among GI cancers in a large community-based oncology network.

Abstract

113 Background: Checkpoint inhibitor (CPI) therapies have shown prolonged survival in patients (pts) with microsatellite instability (MSI). Tumor mutation burden (TMB) has also been associated with benefit from CPIs, with pembrolizumab recently approved for solid tumors with a TMB of ≥10 muts/mb. However, the validity of a tissue-agnostic approach has been debated given the high degree of TMB variation across tumor types. We sought to evaluate the impact of TMB and MSI on CPI response in pts with advanced gastrointestinal (GI) cancers who received NGS profiling. Methods: Patients within the Sarah Cannon network with GI cancer and comprehensive next generation sequencing (NGS) data were identified through Genospace, Sarah Cannon’s clinico-genomic analytics platform. Microsatellite (MS) status [high (MSI-H) vs. stable (MSS)] was defined by NGS. TMB-high (TMB-H) was defined as ≥10 muts/mb. Kaplan-Meier estimates were used to examine time to treatment failure (TTF), defined as the time from therapy start to start of next therapy, death, or loss to follow-up. Results: We identified 5,788 pts with GI cancers who received NGS, of which 48% (N=3,603) had colorectal cancer (CRC). MS status was evaluated on 4,219 (66%) NGS reports, TMB on 2,922 (46%) reports, and both on 2,863 (45%) reports. MSI-H and TMB-H co-occurred on 127 reports (4%), MSS/TMB-H occurred on 312 reports (11%), and MSS/TMB-Low (TMB-L) occurred on 2,424 reports (85%). No reports were MSI-H/TMB-L. Overall, 580 pts (14%) received CPI therapy (N=52 MSI-H/TMB-H, N=41 MSS/TMB-H, N=215 MSS/TMB-L). Independent of line of therapy or tumor type, TTF was significantly shorter for CPI vs. non-CPI therapies [median TTF (mTTF)=151 vs. 238 days, respectively, p=3.4x10-9]. As expected, MSI-H was also associated with longer CPI TTF compared to MSS (mTTF=727 vs. 124 days, p=3.1x10-11). Due to small sample sizes, further analyses were focused on pts with CRC (Table). TMB-H was independently associated with longer CPI TTF compared to TMB-L (Table, p=9.2x10-10). Similarly, the co-occurrence of MSI-H/TMB-H was also associated with longer CPI TTF (Table). However, there was no difference in CPI TTF for MSS/TMB-H and MSS/TMB-L (Table, p=0.45). All pts who received non-CPI therapies, regardless of MS/TMB group, had longer TTF than MSS/TMB-H and MSS/TMB-L pts who received CPI (Table). mTTF [days (N)] for pts with CRC by biomarker. Conclusions: Despite recent tissue-agnostic approvals, TMB does not appear to be a good biomarker of CPI response in pts with CRC. Rather, time to CPI failure is associated with the co-occurrence of TMB-H with MSI-H. Continued research is needed to identify better biomarkers of response to immunotherapy in GI cancers. [Table: see text]