1421PDIMPACT OF PDL1 EXPRESSION ON CLINICAL OUTCOMES IN SUBTYPES OF SARCOMA

ABSTRACT Aim: Sarcomas are rare heterogenous mesenchymal tumors that have limited treatment options. Novel targeted therapies are needed for shifting the paradign of care in sarcomas. Programmed death protein 1 and its ligand PD1/PDL1 axis is an important immunlogical target for cetain tumors and targeting the PDL1 axis may help cause tumor regression . To evaluate the PDL1 expression in subtypes of sarcoma namely osteosarcoma, leiomyosarcoma and Ewings sarcoma and then correlate it with clinicval outcomes. Methods: We evaluated PDL1 expression in three specific subtypes of sarcomas including 161 samples of osteosarcoma, 46 smples of leiomyosarcoma and 33 samples of Ewing sarcoma. Immunohistochemical staining was performed with rabbit primary antibody against PDL1 (CD274/B7-H1) on formalin-fixed paraffin-embedded core sections on tissue microarrays. PDL1 positivity was scored as percentage of cells and immunostain intensity. We also correlated the PDL1 wih clnical outcomes and perfomed subset analyses .We will also perform validation of the PDL1 expression through gene expression analysis using bioinformatics. Results: Of 161 samples of osteosarcoma 36% were positive for PDL1 expression, whilst 97% of 46 samples of leiomyosarcomas and 39% of 33 samples of Ewing's sarcomas were positive for PDL1 expression. PDL1 expression was then correlated with clinical outcomes, gender, age and treatment responses. We are also validating the PDL1 expression by using gene expression data through bioinformatics. .These results will be presented at the meeting. Conclusions: Sarcomas show significant PDL1 expression that may hold potential for justification of a clinical trial with targeted PDL1 inhibitors in the future. Disclosure: All authors have declared no conflicts of interest.