Comprehensive genomic profiling (CGP) to assess mutational load in gastric and esophageal adenocarcinomas: Implications for immunotherapies.

66 Background: Gastroesophageal cancer (GEC) present a management challenge, particularly when ERBB2 is not amplified and cytotoxic therapy has failed. Tumor mutational load is linked to predicted benefit from immune checkpoint inhibitors in advanced cancers. Using CGP we assessed the relationship between mutational burden and clinically relevant genomic alterations in GEC samples in the course of routine clinical care. Methods: DNA was extracted from 40 microns of FFPE sections from patients with GEC. CGP was performed on hybridization-captured, adaptor ligation based libraries to a mean coverage depth of greater than 500x for 236 or 315 cancer-related genes. Mutational load was characterized as the number of somatic base substitutions and short indels per megabase. Samples were stratified by histologic subtype, and presence or absence of therapeutically relevant receptor tyrosine kinase (RTK) alterations. The majority of samples were from patients with advanced disease. Results: The genomic profiles fro...