Comparative Characterization of Tumor Microenvironments in Monophasic and Biphasic Synovial Sarcomas

The impact of histological subtype on immunogenic properties of the tumor microenvironment in synovial sarcomas (SSs) remains understudied. This study aimed to conduct a comparative assessment of tumor microenvironments in monophasic and biphasic SSs. During the study, biomaterial from nine patients with SS was analyzed using IHC analysis, flow cytometry, and real-time PCR. All tumors were infiltrated with CD45+ leukocytes, including the diffusely scattered CD68+ macrophages. FAP+ cells were identified in 7/9 observations, including both monophasic and biphasic tumors. CD4+ T cells and CD20+ B cells were identified by IHC in biphasic SS. The flow cytometry assay revealed significantly higher counts of CD4+ and CD8+ lymphocytes in biphasic SS. IHC revealed E-cadherin expression specifically in the epithelial component of biphasic SS. Vimentin expression in the mesenchymal component of biphasic SS was stronger than in monophasic tumors. The reverse transcription real-time PCR assay revealed higher expression of tumor markers CDKN2A, EGFR, and PDGFRL in monophasic SS. Expression levels of M2 macrophage marker ARG1 and levels of M1 macrophage marker NOS2 in monophasic SS were higher than in biphasic tumors. Biphasic and monophasic SSs revealed distinct molecular patterns and differential degrees of T lymphocyte and M2 macrophage infiltration. Biphasic SSs are characterized by the presence of lymphocytes in the tumor, while monophasic SSs show more pronounced infiltration with M2 macrophages. Monophasic tumors are characterized by higher expression of cancer-related genes CDKN2A, EGFR, and PDGFRL, which can be considered as potential targets for treatment. Our study is limited to a small sample of patients. This is due to the rarity of synovial sarcoma, as well as the fact that we recruited patients who had not received radiation or chemotherapy before taking the biomaterial. It was these criteria that made it possible to objectively assess the state of the tumor microenvironment. © 2025 by the authors.