Immunosuppressive tumor microenvironment in extraskeletal myxoid chondrosarcoma: A case of pleural metastases.

Extraskeletal myxoid chondrosarcoma (EMCS) is an undifferentiated mesenchymal malignancy; however, its immune microenvironment remains to be elucidated. The case of a 34-year-old woman who developed EMCS metastasizing to the pleura is presented here. The pleural EMCS showed hypervascularity, absent PD-L1 expression, and a lack of tumor mutational burden and pathogenic variants. Immunohistological examination of the pleural lesions showed predominant M2 macrophages and sparse CD8+ T cells. EMCS and the tumor stroma were positive for transforming growth factor-β1 (TGF-β1) and vascular endothelial growth factor (VEGF). In contrast, a small number of the stromal vessels were positive for hypoxia inducible factor-1α (HIF-1α). TGF-β1 and VEGF in the tumor stroma and low antigenicity of the tumor cells may help explain how EMCS induced the immunosuppressive microenvironment. These findings may encourage investigators to explore novel combined immunotherapy for EMCS, such as TGF-β1 and VEGF inhibitors, and specific therapy for enhancing tumor antigens.