Background: The discovery of oncogenic mutations as potential targets for cancer therapy has revolutionized the treatment of GIST and other cancers. However, adaptive resistance ultimately develops in nearly all patients, which emphasizes the need for a more detailed understanding of the underlying molecular profile. Methods: Using the Personalis ImmunoID NeXT Platform® (Personalis, Inc.; Menlo Park, CA), an augmented exome/transcriptome platform and analysis pipeline, we performed whole exome sequencing (WES) and whole transcriptome total RNA sequencing (RNA-Seq) of paired baseline tumor and normal tissue. NeXT Liquid Biopsy™ (Personalis, Inc.) was used for WES of plasma-derived ctDNA from serially collected samples collected at baseline, after 1 month and at progression to experimental systemic therapies in 15 patients with advanced/metastatic GIST. Results: WES of tumor tissue samples from all 15 patients confirmed underlying KIT mutation in all patients. There was large heterogeneity of other molecular alterations, which included therapeutically relevant molecular alterations, such as microsatellite instability-high (MSI-high) in 1 sample. RNA-Seq of tumor tissue revealed recurrent overexpression of GALR2, NY-ESO-1 and other genes involved in cancer progression, angiogenesis and anticancer immunity. Patients with response to systemic therapies demonstrated lower levels of cytolytic activity measured by CYT score in tumor tissue compared to patients without response (P=0.04). KIT mutations were detected in serially collected ctDNA samples from 12 (80%) of 15 patients. Quantity of KIT and other mutant ctDNA dynamically tracked the clonal evolution and clinical course during systemic therapy. Conclusions: Comprehensive genomic profiling (WES and RNA-Seq) of tumor tissue and WES of serially collected ctDNA is feasible and detects underlying druggable KIT mutations and other molecular alterations.

Citation Format: Niamh Coleman, Charles Abbot, Neeta Somaiah, Sarina Piha-Paul, Shubham Pant, Jordi Rodon, S. Greg Call, Sean Boyle, Funda Meric-Bernstam, Filip Janku. Whole exome sequencing of tumor tissue and circulating tumor DNA ingastrointestinal stromal tumors (GIST) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr LB057.