Loss of SWI/SNF complex expression (SMARCA4, SMARCA2, SMARCB1, ARID1A) is associated with dMMR in primary adenocarcinoma of jejunum and ileum: A clinicopathological and molecular analysis based on the Chinese population

Objective: The SWI/SNF complex is an important chromatin remodeling complex that has been reported in various tumors. To date, there have been no reports on the subunits of this complex in primary small bowel adenocarcinoma (PSBA). Methods: Hematoxylin & Eosin (H&E) staining slides were reviewed, and the expression of MMR protein, BRM (SMARCA2), BRG1 (SMARCA4), INI1 (SMARCB1), and ARID1A proteins was detected. Molecular genetic testing was performed utilizing the amplification-refractory mutation system (ARMS) and high-throughput sequencing technology. Results: In this cohort of 58 cases, there was a trend toward a female predominance in ARID1A loss (P = 0.084), and BRM (SMARCA2) loss was associated with lymphatic invasion (P = 0.043). A significant positive correlation was observed between ARID1A loss and dMMR (P = 0.021), and BRG1 (SMARCA4) loss was more prevalent in poorly differentiated PSBA (P = 0.023). ARID1A loss was positively correlated with PIK3CA gene mutation (r = 0.551, P < 0.001), and loss of MMR protein expression was also positively correlated with PIK3CA gene mutation (r = 0.354, P = 0.006). Additionally, BRM (SMARCA2) loss showed a significant positive correlation with NRAS gene mutation (r = 0.293, P = 0.025) and a significant negative correlation with KRAS gene mutation (r =-0.281, P = 0.033). Univariate analysis indicated a trend toward poor prognosis with BRM (SMARCA2) loss (P = 0.097). Conclusion: This study represents the initial description of loss of the SWI/SNF complex expression in PSBA, which is rare and primarily originates in the jejunum and ileum. Further investigations are warranted to elucidate potential targets of PIK3CA inhibitors for dMMR PSBA and ARID1A loss of expression in PSBA.