SWI/SNF complex alterations as a biomarker of immunotherapy efficacy in pancreatic cancer

BACKGROUND: Immune checkpoint inhibitors (ICIs) fail to demonstrate efficacy in pancreatic cancer. Recently, genomic biomarkers have been associated with response to ICIs: microsatellite instability high (MSI-H) and tumor mutation burden (TMB) > 10 mutations/Mb. Alterations in Switch/Sucrose Nonfermentable (SWI/SNF) chromatin remodeling genes may predispose to improved outcomes with immunotherapy. The current study examined a possible role for SWI/SNF complex abnormalities in pancreatic cancer responsiveness to ICIs. METHODS: A database of 6831 cancer patients that had undergone next-generation sequencing (NGS) was filtered for advanced pancreatic cancer, SWI/SNF alterations, and outcomes depending on immunotherapy treatment. RESULTS: Nine patients had metastatic pancreatic adenocarcinoma harboring SWI/SNF chromatin remodeling gene alterations and had received ICIs: 7 had an ARID1A alteration (77%); 2, ARID1B (22%); 3, SMARCA4 (33%); 1, SMARCB1 (11%); and 1, PBRM1 (11%). Three patients possessed more than 1 SWI/SNF complex alteration. Only 3 tumors were microsatellite unstable. Eight of 9 patients (89%) achieved an objective response, including a complete remission, with the 2 longest responses ongoing at 33+ and 36+ months. Median progression-free and overall survival was 9 and 15 months, respectively. Responses occurred even in the presence of microsatellite stability, low TMB, and/or low PD-L1 expression. CONCLUSION: A small subset of patients with pancreatic cancer have genomic alterations in SWI/SNF chromatin remodeling components and appear to be responsive to ICIs, suggesting the need for prospective trials. TRIAL REGISTRATION: ClinicalTrials.gov, NCT02478931. FUNDING: Joan and Irwin Jacobs Fund, NIH P30 CA023100 (RK) and LRP KYGF9753 (GPB), the Gershenson, Duarte, and anonymous patient families (GPB).