Arid1a Alterations In Gastrointestinal Cancers As Therapeutic Opportunities.

671 Background: The gene encoding the AT-rich interacting domain (ARID1A) is a tumor suppressor and a subunit of the Switch/Sucrose Non fermentable (SWI/SNF) chromatin remodeling complex that regulates gene expression. Additionally, ARID1A functions to maintain genomic integrity by interacting with ATR. Mutations in ARID1A have been observed in a number of cancers. Inactivation of ARID1A has been reported to lead to increased sensitivity to inhibitors of PARP and PI3K/AKT pathway. We evaluated ARID1A alterations in gastrointestinal (GI) cancers to identify new therapeutic options. Methods: Comprehensive genomic profiling was performed on 55 GI cancer samples with 28 metastatic and 27 primary samples. Targeted sequencing was performed on 562 cancer associated genes in paired tumor and blood DNA samples. Results: ARID1A alterations were noted in 20% (11/55) of GI cancers. Alterations included frameshift and nonsense mutations, INDELs and structural breakpoints which are predicted to cause loss of ARID1A fun...