[Gastric SWI/SNF complex deletion-associated undifferentiated carcinoma with rhabdoid phenotype: a...

Objective: To investigate the clinicopathological features and molecular genetic characteristics of gastric SWI/SNF complex deletion-associated undifferentiated carcinoma with rhabdoid phenotype. Methods: Six cases of gastric SWI/SNF complex deletion-associated undifferentiated carcinoma with rhabdoid phenotype diagnosed at the Henan Cancer Hospital, Zhengzhou, China from January 2019 to December 2021 were collected. Histological observation, immunohistochemical staining, next-generation sequencing, and detection of mismatch repair (MMR), EBER, and HER2 were performed. The clinicopathological and molecular characteristics were summarized and relevant literatures were reviewed. Results: The 6 patients were all male, aged 48-75 years. Their initial symptoms mainly included abdominal pain, melena, and dysphagia. Endoscopic examinations showed gastric ulcer type masses, and the morphology of H&E were similar: the tumor cells showed diffuse infiltrating growth, no specific structural characteristics, obvious cell atypia, obvious mitoses, and rhabdomyoid cells with unequal proportions of eosinophilic cytoplasm. The immunohistochemistry for CKpan was negative in 3 of the 6 cases, while focal expression of other epithelial markers was found, including EMA (6/6), CK8/18 (4/6), and CK7 (1/6). P53 was diffusely strong positive in 4 cases (4/6), and negative in 1 case (1/6). Ki-67 was highly expressed (positive rate range, 60%-90%). Other related markers such as mesenchymal tumors, lymphoma, melanoma and germ cell tumors were all negative. Detection of the SWI/SNF complex subunit, namely INI1 (SMARCB1), BRG1 (SMARCA4), ARID1A protein detection, was detected in 5 cases with no SMARCA4 expression (5/6), 1 case with no ARID1A expression (1/6), and all cases with SMARCB1 expression (6/6). MMR proteins were examined, and dMMR was found in 1 of the 6 cases. HER2 expression was 0 in 3 cases, 1+ in 1 case, and 2+ in 2 cases, while no amplifications of HER2 gene were detected using FISH. EBER was negative in all 6 cases. Among the 4 cases of surgical radical treatment that were subject to next-generation sequencing, 3 cases showed TP53 mutations; 1 case showed ARID1A gene frame shift mutation, and there were also mutations of ATM, PTEN and other genes. There was 1 case with detected SMARCA4 gene copy number variant, and other gene mutations such as ALK, BRAF, CDKN1B, BRCA2, etc. Conclusions: Gastric SWI/SNF complex deletion-associated undifferentiated carcinoma with rhabdoid phenotype is a poorly differentiated and rare tumor. Detection of SWI/SNF complex related proteins is helpful for its diagnosis. Moreover, gene mutations associated with SWI/SNF complex will become a new indicator for its diagnosis and prognostication, and a potential new target for molecular therapy, which deserves more attention and warrants more research.