BACKGROUND: Clear cell (hemangioblastoma-like) stromal tumor of the lung (CCSTL) is a rare pulmonary neoplasm. Recently, 9 cases of CCSTL harboring the YAP1-TFE3 gene fusion have been described, and it has been suggested that this aberration could be a characteristic feature of this tumor. CASE PRESENTATION: We here report another case of CCSTL in a 57-year-old male, which presented as a solitary lung nodule 45 mm in the greatest dimension. Microscopically, the tumor consisted of epithelioid to spindled cells with mild-to-moderate nuclear atypia, finely granular or vesicular chromatin, and small nucleoli. Nuclear indentations were a common finding. There were up to 3 mitoses per 10 HPF. The cytoplasm was slightly eosinophilic or clear. Scattered non-tumor large multinucleated cells were present. Immunohistochemically, the tumor cells showed diffuse positivity for TFE3, CD10, vimentin, and IFITM1. Other markers examined were negative, and the expression of lineage-specific markers was not found. NGS analysis revealed a fusion transcript of the YAP1 and TFE3 genes, and a pathogenic variant of the MUTYH gene. CONCLUSION: Our finding supports the recent data suggesting that CCSTL represents a distinct entity characterized by the recurrent YAP1-TFE3 fusion.

Department of Abdominal Thoracic Surgery and Traumatology 1st Faculty of Medicine Charles University and General University Hospital Prague U Nemocnice 2 128 00 Prague 2 Czech Republic

Department of Pathology 1st Faculty of Medicine Charles University and General University Hospital Prague Studničkova 2 128 00 Prague 2 Czech Republic

Department of Pathology and Molecular Medicine 3rd Faculty of Medicine Charles University Thomayer Hospital Prague Czech Republic

Department of Pathology Charles University 3rd Faculty of Medicine University Hospital Kralovske Vinohrady Prague Czech Republic

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