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Introduction: Soft tissue sarcomas (STSs) are malignant tumors arising from mesenchymal tissues. Patients with advanced and metastatic STSs have low overall survival rates and relatively limited treatment options. Oncostatin M (OSM) is a pleiotropic cytokine that was shown to carry both pro- and anti-tumorigenic properties in various cancer types. However, the role of OSM in STSs has not yet been elucidated. Moreover, the potential additive effects of combining OSM and anti-PD-1 therapy have not been carried out so far. Methods: The aim of this study was to determine the effects of in vitro OSM administration on liposarcoma, leiomyosarcoma, and myxofibrosarcoma immune cells isolated from peripheral blood and tumor tissues and the potential cooperative nature of OSM and nivolumab in treating these STSs. We designed a cohort study to explore novel histology-driven therapies in our target STSs. The immune cells were isolated from the peripheral blood and tumors of patients with STS, and the proportions and phenotypes of immune cells were evaluated with flow cytometry after cultivation with therapeutic monoclonal antibodies. Results: The proportion of peripheral CD45+ cells was not affected by OSM but was significantly increased by nivolumab, whereas both treatments had an effect on CD8+ T cells. In tumor tissues, CD8+ T cell and CD45‒ TRAIL+ cell cultures were boosted by nivolumab and significantly enriched by OSM. Our data suggest that OSM may play a role in the treatment of leiomyosarcoma, myxofibrosarcoma, and liposarcoma. Conclusion: In conclusion, the biological efficacy of OSM is reflected in the tumor microenvironment rather than in the peripheral blood of the patients in our cohort, and nivolumab could potentiate its mechanism of action in selected cases. Nevertheless, more histotype-tailored studies are needed to fully understand the functions of OSM in STSs.

IntroductionSolitary fibrous tumor (SFT) is an extremely rare disease with a high misdiagnosis rate and a potentially malignant biologic nature. We have collected and analyzed data from 18 SFT patients to provide a deeper insight into this uncommon disease entity.MethodsIn our study, 18 patients who had undergone surgery between April 2014 and December 2021 for the diagnosis of SFT were evaluated. The collected data for each patient included the location of the SFT, the preoperative diagnosis, the definitive histological diagnosis, the presence of postoperative complications, the time of recurrence, the time of systemic progression, the type of treatment, and the survival rate. The median follow-up was 36 months.ResultsIn three patients, the preoperative diagnosis did not correlate with the definitive histology of SFT. In patients with the limb location of SFT, no signs of recurrence nor distant metastases were seen within the study period. In total, 50% of the postsurgical complications were associated with the abdominal location of the SFT. In newly diagnosed SFT patients, two patients (20%) developed local recurrence, and the median time until recurrence was 22.5 months. Out of patients that were admitted and operated on for recurrent SFT, 67% relapsed, and the median time to relapse was 9.5 months. The systemic progression of the disease was observed in 33% of patients treated for recurrent SFT.ConclusionIn our study, the misdiagnosis rate was high and correlated with previously published studies. Postsurgical complications were associated with the extrathoracic location of SFT. The mainstay of SFT treatment remains radical surgery, although radiotherapy alone can significantly improve overall survival. Clinical trials are urgently needed to evaluate the potential effect of other treatment modalities, such as immunotherapy and targeted therapy, in SFT patients.

The treatment options for metastatic soft tissue sarcomas (STSs) are limited. In most cases, immunotherapy with immune checkpoint inhibitors has not been successful so far. Macrophages dominate the immune landscape of STSs; thus, combinatorial strategies aiming at both tumor-infiltrating lymphocytes and macrophages may represent a particularly relevant treatment approach for metastatic or recurrent STSs.In this cohort study, 66 patients who underwent surgery for STSs were enrolled. Tumor cells and tumor-infiltrating immune cells were analyzed using flow cytometry and immunohistochemistry. In cell suspensions obtained from surgical resections, human T cells were activated by superparamagnetic polymer beads and cultured at a concentration of 0.3 × 10The most profound response to anti-CD47 therapy was observed in an undifferentiated pleiomorphic sarcoma which also displayed high expression of CD47 in the tumor microenvironment. Both anti-PD-1 and anti-CD47 therapies drastically increased the production of pro-inflammatory cytokines in the tumor microenvironment of STSs, but co-administration of both agents did not further increase cytokine secretion. Furthermore, all patient samples treated with a combination of both anti-PD-1 and anti-CD47 antibodies showed a dramatic reduction in cytokine secretion.Our findings suggest that anti-PD-1 and anti-CD47 therapies do not enhance each other, and the combined application of anti-PD-1 and anti-CD47 agents in vitro limits rather than potentiates their efficacy.

e23560 Background: Soft tissue sarcomas (STSs) are rare mesenchymal tumors. With more than 70 histological subtypes of STSs, studies defining robust biomarkers of therapeutic value are lacking. Even with the improvements in local control rates, metastases and death occur in 50% of patients that are diagnosed with high-risk STSs. Across nearly all sarcoma types, macrophages dominate the immune landscape of STSs. While immune checkpoint inhibitors (ICIs) represent the major immunotherapeutic approach in malignancies with a high load of T cells, the anti-CD47 anti-cancer therapy mostly promotes macrophage-mediated phagocytosis. The efficacy of both therapies is critically dependent on the composition of the tumor microenvironment. Methods: In our study, we evaluated the potential additive effects of combining the anti-PD-1 immunotherapy and anti-CD47 immunotherapy ex vivo. The proportions of tumor cells and tumor-infiltrating lymphocytes were characterized ex vivo from resected tumors of 73 patients who underwent surgery for STS. The expression of CD47 on tumor cells was analyzed by immunohistochemistry. Cell suspensions were obtained from freshly resected tumors and the proportions of CD45+, CD45-, CD3+, CD4+, and CD8+ cells were measured by flow cytometry. The effect of the anti-PD-1 blockade, anti-CD47 blockade, and the combinatorial application of anti-PD-1 and anti-CD47 therapies on the immune cell activation in vitro was investigated by culturing of cell suspensions at a concentration 0.3x106/ul in the presence/absence of therapeutic monoclonal antibody (Nivolumab 2 ug/ml; anti-CD47 clone MIAP410 20ug/ml) and evaluated by a cytokine Luminex assay (Milliplex® MAP Human Cytokine Bead Panel (Sigma Aldrich) for TNFα, IFNγ, and IL-2 cytokines analysis). Results: The addition of anti-PD1 to CD3/CD28 stimulation drastically increased the production of all cytokines analyzed. This increase in pro-inflammatory cytokine secretion was even more pronounced after adding an anti-CD47 monoclonal antibody to the cell culture. However, a combinatorial application of anti-PD-1 and anti-CD47 agents in vitro was found to limit rather than potentiate the immune activation in the TME of human STS. On an individual level, the most profound response to anti-PD-1 was observed in high-grade leiomyosarcoma and the most profound response to anti-CD47 therapy was observed in an undifferentiated pleiomorphic sarcoma. Conclusions: Our data suggest that combinatorial strategies based on ICIs and anti-CD47 blockade may not provide the desired outcome in STSs. Both therapies, anti-PD-1, and anti-CD47 alone, could however bear a therapeutic potential in selected tumors after close evaluation of the CD47 and PD-1 expression status, as well as the extent of T cell/macrophage infiltration.