35P Beyond microsatellite testing: Tumor mutational burden, should it be routine in patients with GI cancers?
Annotatsiya
Implementation of Immune checkpoint inhibitors into clinical practice started a new era of cancer treatment. However up today there are only 2 main predictors of efficacy of immunotherapy performed routinely MSI and PDL1 (CPS) testing. Nevertheless, real world practice often forces to search new biomarkers that can predict efficacy of ICI therapy in cancer treatment. We explored 480 formalin embedded tissues with GI cancers that all had microsatellite stable status (MSS) and CPS ≤ 5. To assess TMB status we used FMI testing panel. TMB-high was defined – more than 10 muts/mb. From 480 samples – 23 (4,8%) were esophageal cancer, gastric cancer – 40 (8,3%) cases, right sided colorectal cancer – 177 (36,9%) cases, left sided – 240 (50%) cases. Out of 480 (100%) microsatellite stable tumors 35 (7,3%) cases were confirmed as TMB-high tumors. Subgroup analysis revealed that none of 23 esophageal cases were TMB-high, from 40 cases of gastric cancer only 2 (5%) patients had TMB-high status. In 177 right sided colorectal cancers TMB high status was found in 12 (6,7%) cases. Most frequently TMB high status in MSS tumors were found in left sided colorectal cancer 21 (8,75%) out of 240 samples (p≤0.005). Routinely TMB assessment identifies nearly 7,3% of GI cancers as MSS/TMB-high. Subgroup analysis clearly showed that patients with colorectal cancer had higher incidence of TMB high status. This subgroup may expand the population of GI cancers who may benefit from immune checkpoint inhibitor based therapeutic approaches.