Intratumoral heterogeneity as a predictive biomarker in immunotherapy for advanced esophageal cancer

e16059 Background: Previous studies have shown that the acquired resistance to anti-cancer therapy is largely due to intratumoral heterogeneity (ITH), thus leading to unfavourable prognosis. As known, there is no comprehensive research using ITH as a biomarker to predict the efficacy of immunotherapy in advanced esophageal cancer (ESCA) patients. Methods: Bioconductor R package Maftools was used to analyze somatic variants of advanced ESCA from MSK-IMPACT-1611 study cohort (PMID: 30643254) with data from 39 patients. We then used a mutant-allele tumor heterogeneity (MATH) algorithm to measure ITH score and analyzed the difference in the genetic profile between the ITH score high (ITH-H) and ITH score low (ITH-L) groups, the association with tumor mutational burden (TMB), and the effect of ITH on the prognosis of immunotherapy. Results: There were significant differences in gene mutation spectrum between ITH-H and ITH-L groups. The genes with the highest mutation frequency in ITH-H group were TP53 (93.75%), CDKN2A (37.5%), PREX2 (31.25%), PTPRD (25%), ALK (18.75%), ERBB4 (18.75%), and KMT2D (18.75%), while the genes with the highest mutation frequency in ITH-L group were TP53 (69.57%), CDKN2A (21.74%), PIK3CA (21.74%), APC (17.39%), ARID1A (17.39%), LATS1 (17.39%), and RNF43 (17.39%).There was significant difference in median overall survival (mOS) between ITH-L and ITH-H groups (not reach versus 5 months, hazard ratio (HR) = 3.96, 95%CI 1.02−15.39, P = 0.034). There was no significant difference in median TMB levels between ITH-L and ITH-H groups (7 Muts/Mb versus 8 Muts/Mb, P = 0.09). The TMB high (TMB-H) patients had no significantly better mOS than the TMB low (TMB-L) group (HR = 0.27, 95%CI 0.06−1.26, P = 0.072). A pooled analysis of ITH and TMB show that mOS in the ITH-L+ TMB-H group was significantly better than that in the ITH-L+TMB-L, ITH-H+TMB-H, and ITH-H+TMB-L group (HR = 2.03, 95%CI 0.06−7.69, P = 0.002). Conclusions: The results suggest ITH is a predictor of ESCA immunotherapy efficacy independent of TMB.