Evaluation of somatic and germline variants in patients with small bowel adenocarcinoma reveals clinically actionable targets.

4159 Background: Small bowel adenocarcinoma (SBA) is a rare gastrointestinal cancer with a poor prognosis and limited treatment options. Because the treatments for colorectal cancer showed limited efficacy in SBA, the NCCN guide strongly encourages SBA patients to participate in clinical trials. In this study, we aimed to explore clinically actionable variants in a large cohort of patients with SBA to assist oncologists to select the matched trials for patients. Methods: To explore therapeutic targets in 84 Chinese SBA patients, a deep sequencing panel (OncoPanscan, Genetron health) was used to characterize somatic alterations including point mutations, indels, copy number alterations, gene fusions as well as pathogenic germline variants. Results: Recurrent somatic mutations included TP53 (57%), KRAS (56%), APC (31%), SMAD4 (21%), MDM2 (13%), CTNNB1 (12%), KMT2C (12%), SOX9 (12%), ARID2 (12%), FAT3 (11%), FBXW7 (10%), SPTA1(10%) and PIK3CA (10%). Of the entire cohort, we observed five activating PIK3CA mutations (R108H; G364R; E542K; E545K, n = 2) which may be sensitive to FDA-approved PIK3CA inhibitor alpelisib. Additionally, patients with loss-of-function mutation in NF1 (n = 2), STK11 (n = 1) and PTEN (n = 1) can be targeted with MEK inhibitor selumetinib and mTOR inhibitor everolimus, respectively. Except for one V600E mutation, all mutations in BRAF are either type 2 (L597R, n = 1) or type 3 (N581S, n = 1; D594N, n = 4) which were sensitive to MEK inhibitor trametinib. We also found four type 2 MAP2K1 activating mutations (K57E, K57N, and F53L) which can be targeted by trametinib. Furthermore, oncogenic ERBB2/HER2 mutations were seen in 4 patients including S310F (n = 1), V842I (n = 2) and V777L (n = 1). We also found one patient harbored ERBB2/HER2 high magnification amplification. These five patients were candidates for HER2-targeted therapy clinical trials. Interestingly, one IDH1 mutation (R132C) carrier in our cohort might benefit from ivosidenib. In addition, we observed targetable gene amplification of MDM2 (n = 2) and FGF3/4/19 (n = 2). There were two patients with MLH1 loss-of-function germline mutations that may benefit from immunotherapy. Among 78 patients with available MSI status, three were designated as microsatellite instability. The median TMB of microsatellite stable patients was 2.82 mutations/Mb. Lastly, we observed five deleterious germline mutations, three for SBDS, one each for APC and ERCC5. Taken together, at least 33 (39%) patients in our cohort harbored actionable genetic alterations. Conclusions: Through comprehensive genomic characterization of Chinese SBA patients, we identified actionable variants of multiple signaling pathways in plenty. NGS profiling results can guide physicians to enroll a significant portion of SBA patients in genomically-matched clinical trials.