Abstract:Objective To investigate the clinicopathological features, diagnosis and differential diagnosis of 2 cases of SMARCA4 (SWI/SNF related, Matrix Associated, Actin Dependent Regulator of Chromatin, Subfamily A, Member 4)-deficient tumors. Methods Two cases of SMARCA4-deficient tumor in Qingdao Hospital of Chinese Medicine from June 2018 to November 2019 were selected. The pathological features were reviewed. The expressions of SMARCA4/BRG1, AE1/AE3, Ki-67 and Syn were detected by immunohistochemistry. The correlation between pathological features and immunohistochemical phenotype of the two cases was analyzed and discussed with literature review. Results Pathological results confirmed that 1 case was SMARCA4-deficient undifferentiated sarcoma and 1 case was SMARCA4-deficient hypercalcemia small cell carcinoma. These two cases were similar in histopathological morphology. Under low power microscopy, tumor cells showed diffuse infiltration or nest like growth, often growing around blood vessels, and tumor necrosis was obvious. Under high magnification, the tumor cells were mainly rhabdoid or epithelioid, with eosinophilic or transparent cytoplasm, round nucleus, obvious nucleolus and mitotic figures. Immunophenotype showed that SMARCA4/BRG1 were absent in both 2 cases, cytoplasm Vimentin and localized Syn were positive, and AE1/AE3 was negative, Ki-67 was 60% in one case and 80% in the other one. Conclusion SMARCA4-deficient tumors have some similarities in pathological morphology and immunohistochemical expression, which need to be analyzed and confirmed by more cases. 