Abstract 4134: Immune infiltration and PD-L1 expression in the tumor microenvironment are prognostic in osteosarcoma

Abstract

Abstract Purpose: Over the past four decades, osteosarcoma (OS) survival rates have remained stagnant. There is a need to identify novel therapies to target OS. In this study we examined the expression of Programed Death Ligand 1 (PD-L1) and defined the tumor microenvironment in OS in order to assess the feasibility of utilizing immune checkpoint inhibitors as a treatment modality. Experimental Design: PD-L1 expression in OS was examined in two patient cohorts using immunohistochemistry (IHC) (n = 48, n = 59) and expression was validated using quantitative real time PCR (qRT-PCR) (n = 21) and western blotting (n = 9). IHC was used to determine presence of tumor infiltrating lymphocytes and antigen presenting cells (APCs) in the tumor. Expression of PD-L1 was correlated with the presence of immune cells and with event free survival in OS. Results: PD-L1 is expressed in up to 25% of primary OS tumors. Of the PD-L1 positive tumors the majority were also PD-1 positive (92% vs 8%, p = 0.002). In addition, the presence of immune cells in the tumor mass was significantly associated with PD-L1 expression. Although all immune cell types examined were present in OS, only infiltration by APCs, specifically CD1a positive dendritic cells (48.6% vs. 51.4%, p = 0.0010) and CD68 positive macrophages (70.3% vs. 29.7%, p = 0.0316), was associated with worse outcomes. PD-L1 expression was significantly associated with worsened survival (21.6% pos. vs. 78.4% neg., p = 0.0146). Conclusions: For the first time we have identified PD-L1 expression or presence of CD1a or CD68 positive antigen presenting cells as prognostic markers for worsened outcome in OS. Furthermore, we show that IHC is a valid detection method for PD-L1 in OS. With up to 25% of OS patients expressing PD-L1, this study provides rational for targeting the PD-L1:PD-1 axis for immunotherapy in OS. Citation Format: Pratistha Koirala, Michael Roth, Jonathan Gill, Jordan Chinai, Sajida Piperdi, David Geller, Bang Hoang, Vincent Poon, Xingxing Zang, Richard Gorlick. Immune infiltration and PD-L1 expression in the tumor microenvironment are prognostic in osteosarcoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4134.