1709PThe immune landscape of chondrosarcoma reveals an anti inflammatory environment

Abstract Background In many solid tumors, the setting of an immunosuppressive environment regulated by macrophages and immune checkpoints (ICP) is often a bad prognosis factor. Thus, targeting this immune environment led to the developments of new immunotherapies that raised high hopes for the treatment of solid tumors. Immunotherapy for chondrosarcoma (CHS) is comparatively less advanced partly because the immune environment of these rare tumors remains sparsely explored. However with their high resistance to conventional therapies CHS are typically tumors for which immunotherapies could be a solution. To get an exhaustive cartography of CHS immune landscape, identify prognosis factors and therapeutic targets, we described the immune populations and immune checkpoints of conventional CHS (CCHS) and dedifferentiated CHS (DD CHS), one of the rarest and most aggressive subtype of CHS. Methods Immunohistochemical methods (IHC) were used to map the expression of immune cells markers (CD3, CD8, CD68, CD163) on a cohort of 27 CCHS and 49 DD CHS. RT-qPCR was used to screen the expression of a panel of ICP, for the most promising ones, their expression was confirmed by IHC. The impact of the density of Tumor Infiltrating Lymphocytes (TIL), Tumor Associated Macrophages (TAM) and ICP on clinical outcome were analyzed. Results TAM were the main immune population encountered in DD and CCHS. Immune infiltrate composition was correlated with DD CHS’ outcome: a high CD68+ TAM density was associated with the presence of metastases at diagnosis (p  Conclusions By showing that CHS immune environment is mainly composed of macrophages expressing CSF1R and that a high CD68 intratumoral density is correlated with the presence of metastases at diagnosis; our data reinforce the hypothesis of an immunosuppressive environment of this tumor. Our results converge to indicate that an immunomodulation through macrophages could be a promising therapeutic approach for CHS. Legal entity responsible for the study The authors. Funding Liddy Shriver; University of Lyon Claude Bernard 1. Disclosure All authors have declared no conflicts of interest.