Abstract

ABSTRACT Background SMARCA4 is a component gene of the SWI/SNF (SWItch/Sucrose NonFermentable) chromatin remodeling complex; undifferentiated tumors associated with its functional deletion have been described in several organs. However, no established treatment for these tumors currently exists. Case In this study, we report a case of a SMARCA4‐deficient undifferentiated urothelial carcinoma with high PD‐L1 expression that was effectively treated with nivolumab after early relapse following treatment for non‐invasive bladder cancer. The histological morphology of the rhabdoid‐like undifferentiated tumor of unknown primary led us to suspect a SWI/SNF‐deficient tumor, and subsequent immunostaining led to the diagnosis of a SMARCA4‐deficient undifferentiated tumor. This effort also led to the identification of the developmental origin of this SMARCA4‐deficient undifferentiated tumor as a non‐invasive bladder cancer. We also carried out a detailed immune phenotypic assay on peripheral T cells. In brief, a phenotypic change of CD8+T cells from naive to terminally differentiated effector memory cells was observed. Conclusion Regardless of the organ of cancer origin or cancer type, SWI/SNF‐deficient tumors should be suspected in undifferentiated and dedifferentiated tumors, and immune checkpoint inhibitors may be considered as a promising treatment option for this type of tumor. The pathogenesis of SMARCA4‐deficient anaplastic tumors awaits further elucidation for therapeutic development.