Mesenteric SMARCA2-Deficient Yet SMARCA4-Preserved Aggressive Undifferentiated Tumor: A Case Report

The SWItch Sucrose Non-Fermentable (SWI/SNF) chromatin remodeling complex, which includes components such as SMARCA4 and SMARCA2, regulates gene expression by controlling chromatin compaction and accessibility in an ATP-dependent manner. These components are also implicated in carcinogenesis. Thoracic SMARCA4-deficient undifferentiated tumor is a recently introduced category in the fifth edition of the WHO classification in 2021, typically exhibiting rhabdoid morphology in adults. In contrast, rhabdoid tumors occurring within the abdominal cavity in adults are rare and sporadic, with limited detailed documentation, making them relatively less understood compared to their thoracic counterparts.

A man in his 70s was admitted to our hospital with a chief complaint of fever. He was diagnosed with a mesenteric solid tumor measuring 6 cm in maximum diameter. Shortly after the hospitalization, bowel obstruction became evident, accompanied by the rapid tumor progression, and then surgical treatment was attempted. A soft, bulky tumor situated in the mesentery accompanied by extensive tumor dissemination was found intraoperatively. The tumor was resected along with the obstructed terminal ileum, aiming to restore intestinal patency and obtain tissue samples. Histopathologically, the tumor represented morphological features resembling a rhabdoid tumor along with a high Ki67 labeling index (50%). Immunohistochemistry revealed SMARCA2 deficiency with preserved SMARCA4 expression. The absence of Claudin-4 expression further supported the diagnosis of a mesenteric SMARCA2-deficient yet SMARCA4-preserved undifferentiated tumor. The patient succumbed 20 days after surgery due to aggressive peritonitis carcinomatosis.

To the best of our knowledge, this is the first case report of a mesenteric undifferentiated tumor with rhabdoid cytomorphology due to SWI/SNF chromatin remodeling complex deficiency caused by isolated SMARCA2 deficiency. The tumor, in our case, arose in the abdominal organs and appears to share a similar oncogenic process with the category of thoracic SMARCA4-deficient undifferentiated tumors in the WHO classification. Further research is required to improve our understanding of its clinical features, underlying mechanisms, and optimal management strategies.