Abstract 5714: Characterization of SWI/SNF complex gene mutations, protein expression and tumor immune microenvironment in cholangiocarcinoma

Abstract Introduction: Cholangiocarcinoma (CCA) is a rare tumor accounting for less than 2% of all human malignancies. Mutations in the mammalian Switch/Sucrose Non-Fermentable (SWI/SNF) chromatin remodeling complex have been identified in approximately 20% of all human cancers and more than 40% of CCA. If the role of SWI/SNF on the tumor biology and microenvironment is being uncovered in other tumor types, it remains vastly unknown in CCA. Here, we wanted to investigate, using clinical samples, the association between SWI/SNF defects, the molecular landscape and tumor immune microenvironment in CCA. Material and Methods: Mutation profiling of 103 patients with CCA from Gustave Roussy (GR) was assessed with FoundationOne® CDx 324-gene NGS panel. Formalin-fixed paraffin-embedded tumor tissues from 11 patients with CCA were analyzed for SWI/SNF (PBRM1, ARID1A, SMARCB1 and SMARCA4) and Polycomb-DUB (BAP1) subunits, as well as lymphocytic markers (CD4 and CD8). Stainings were performed using a VENTANA BenchMark ULTRA. Absolute count of positive cells per mm2 was determined by digital image analysis with the Definiens Developer XD™ by selecting at least 5 independent tumoral zones. Pairwise comparisons were performed using the Mann-Whitney test. Results: Among the patients for whom NGS data was available, the most frequently altered genes were TP53 (27%), CDKN2A (17%), KRAS (16%), ARID1A (12%), FGFR2 (12%) and PBRM1 (10%). Subunits of the SWI/SNF complex and BAP1 were mutated in 25% and 10% of cases, respectively. Tumor samples with ARID1A mutations (n=5) showed strongly decreased ARID1A expression compared to WT tumor samples (n=2) (mean = 308.03 positive nuclei (p.n)/mm2 versus 6096.82 p.n/mm2 respectively; P<0.0001) but unchanged PBRM1, SMARCB1 and SMARCA4 expression. PBRM1 mutations (n=4) were associated with decreased expression of PBRM1 (mean = 309.6 p.n/mm2 versus 4980.2 p.n/mm2 in WT samples; P<0.0001) and ARID1A (mean=1196.15 p.n/mm2; P<0.001), but unchanged SMARCB1 and SMARCA4 expression. BAP1 mutations (n=3) were also associated with decreased BAP1 and ARID1A expression (ARID1A mean = 457.70 p.n/mm2; P<0.001). ARID1A and PBRM1-altered tumor samples showed a poorly infiltrated microenvironment, with decreased CD4+ T cell (159.48 positive cells (p.c)/mm2 and 188.66 p.c/mm2 respectively versus 1126.52 p.c/mm2 for WT; P<0.0001) and CD8+ T cell density (72.38 and 76.54 p.c/mm2 versus 548.58 p.c/mm2 for WT; P<0.0001). Conclusion: Mutations in the ARID1A and PBRM1 subunits of the SWI/SNF complex are associated with a loss of protein expression. In contrast to what reported in other tumor types, ARID1A and PBRM1 mutations correlated with poorly lymphocytic TIME in CCA. Decreased PBRM1 expression is further associated with decreased ARID1A expression. Independent revalidation and further study in larger tumor series are warranted. Citation Format: Clémence Astier, Jean-Yves Scoazec, Virginie Marty, Olivia Bawa, Nicolas Signolle, Carine Ngo, Francesco Facchinetti, Antoine Hollebecque, Sophie Postel-Vinay. Characterization of SWI/SNF complex gene mutations, protein expression and tumor immune microenvironment in cholangiocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5714.