LAUSR

BACKGROUND Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor with high prevalence of KIT and PDGFRA mutations. Few effective treatments can be exploited in imatinib or sunitinib resistant cases. While in immunotherapy, application of the highly individualized cancer neoantigen vaccines is hampered due to high economic and time cost. In this study we identified the most frequent mutation in Chinese GIST patients and predicted candidate neopeptide by next generation sequencing (NGS). METHOD Tumor tissues and matched blood samples of 116 Chinese GIST patients were collected. Genomic profile was detected through NGS and 450 cancer genes were deeply sequenced. KIT mutations were identified and long peptides containing the mutation were queried in NetMHCpan 4.0 tools to predict MHC class I binding of mutant peptides. RESULTS The most frequent mutated genes in detected GIST patients were KIT (81.9%, 95/116), CDKN2A (18.97%, 22/116) and CDKN2B (15.52%, 18/116) in this cohort. The most common mutation of KIT was A502_Y503 duplication (15.93%, 18/113) in exon 9. Among 116 cases, 103 were HLA I genotyped and 101 were HLA II genotyped. In total, 16 samples with the mutation of KIT p.A502_Y503dup were identified to produce neoantigens with qualified HLA affinity. CONCLUSION KIT hotspot mutation (p.A502_Y503dup) has the highest incidence, which may further eliminate the need for whole genome sequencing and patient-specific neoantigen prediction and synthesis. Therefore, for those carrying such mutation, accounting for around 16% of Chinese GIST patients, and are usually less sensitive to imatinib, effective immunotherapies are in prospect.