A case report of a novel inflammatory and incarcerated testicular stromal tumor associated with the EWSR1::ATF1 gene fusion

Background This case report describes a novel subtype of testicular sex cord-stromal tumor, termed the “inflammatory and nested testicular sex cord tumor”, which is characterized by a specific EWSR1::ATF1 gene fusion. We present the clinicopathological features of this case to enhance the understanding of this extremely rare tumor. Case presentation A 45-year-old male patient presented with a right testicular mass that had been present for six years without an identifiable cause. MRI conducted revealed a round nodule in the right testicular area, measuring approximately 38 × 28 mm, with relatively well-defined margins. The tumor exhibited a nodular growth, consisting of epithelial-like cells with abundant clear cytoplasm arranged in solid nests or sheets. Fibrous connective tissue surrounded the epithelial-like tumor nests, and focal inflammatory cell infiltration was observed within the stroma and tumor periphery. Immunohistochemistry showed membranous positivity for α-inhibin in the epithelial-like component. Molecular testing revealed an EWSR1::ATF1 gene fusion, leading to a final diagnosis of inflammatory and nested testicular sex cord tumor. Conclusions We report a novel subtype of testicular sex cord-stromal tumor, distinct from conventional forms, characterized by nest-like growth of clear epithelial-like tumor cells, focal inflammatory cell infiltration, and the presence of the EWSR1::ATF1 gene fusion. This case provides further evidence that supports the fusion pattern and clinicopathological basis for the newly proposed subtype of testicular sex cord-stromal tumor, inflammatory and nested testicular sex cord tumor.