LAUSR

e22548 Background: Clinical responses in patients with soft tissue sarcoma administered immune checkpoint inhibitors have been infrequent. Little is known regarding the immune microenvironment in soft tissue sarcoma that leads to a lack of effective responses with immune therapies. Whilst several studies have shown T cell infiltration in sarcomas, these tumors do not respond to immunotherapies. Macrophages are important regulators of immune responses in the tumor microenvironment. Studies in mouse models indicate that macrophages regulate immune checkpoint inhibitor response. With the overall goal of developing more effective combination immunotherapies for sarcoma, we examined tumor associated macrophages in patients with soft tissue sarcoma administered neoadjuvant chemotherapy. Interactions between macrophage infiltration, tumor immunogenicity and overall survival were also assessed using publicly available RNAseq and exome mutation data. Methods: Immunohistochemistry was performed on formalin fixed soft tissue sarcoma tissue. Tissues from 20 patients with soft tissue sarcoma pre and post neo-adjuvant chemotherapy were included. TAMs were detected by CD68; M2 subtype were detected by CD163. CD4, CD8, and CD25 T cells were also examined. The density of CD68+ TAMs, CD163+ TAMs and the ratio of CD163+ TAMs / CD68+ TAMs were calculated and their correlation with survival was also made. Publicly available RNAseq and exome mutation data were assembled from The Cancer Genome Atlas (TCGA) sarcoma cohort (n = 259). For each tumor, a relative measure of abundance of tumor-infiltrating macrophages was estimated using gene expression. Tumor mutational burden (TMB), expressed as the rate of non- synonymous mutations per megabase of sequenced DNA, was used as a measure of tumor immunogenicity. Interactions between macrophage infiltration, tumor immunogenicity and overall survival were assessed by Cox regression and Kaplan-Meier analysis. Categorical relationships involving clinical, immunologic, and genomic features of the tumor immune subclasses were compared. Results: Specific alteration in the density of CD68+ TAMs, CD163+ TAMs, and the CD163 / CD68 ratio were observed in patients with soft tissue sarcoma responding to neoadjuvant chemotherapy. Categorical relationships involving macrophage infiltration, TMB, and survival were also observed. Conclusions: These study support the targeting of tumor associated macrophages in patients with soft tissue sarcoma and suggest that changes in TAMs may be achievable using neoadjuvant chemotherapy.