Abstract 2621: Microsatellite instability is a potential biomarker for immune checkpoint inhibitor in endometrial cancer

Abstract

Abstract [Introduction] In recent years, tumor cells have immune escape mechanism and immune checkpoint inhibitor therapy (anti PD-1/ PD-L1 antibody) has shown benefit in various cancers. Somatic mutations have the potential to encode ‘’non-self’’immunogenic antigens and lymphocytes infiltrate tumor cells in Microsatellite-instable (MSI) endometrial cancers. Therefore, immune checkpoint inhibitor therapy might be effective in MSI endometrial cancers. [Method] Mismatch repair protein (MLH1, PMS2, MSH2, and MSH6), tumor-infiltrating lymphocytes (CD8), and PD-1/PD-L1 expression were assessed by immunohistochemistry in 60 patients with endometrial cancer. We examined whether MSI status have enhanced immune microenvironment and become the therapeutic effect predictor of PD-1/PD-L1 immunotherapy in endometrial cancer. [Results] Loss of mismatch repair protein (MSI group) was identified in 8 (13.3 %) of 60 patients with endometrial cancer. Expression of tumor-infiltrating lymphocytes (CD8) and PD-L1/PD-1 were significantly higher in MSI group compared to MSS group (p=0.001, p=0.044 and p=0.013). [Conclusion]These results suggested that immune checkpoint inhibitor (anti PD-1/PD-L1 antibody) is effective in endometrial cancers with MSI. MSI testing is likely to be a biomarker for PD-1/PD-L1 immunotherapy in endometrial cancer. Citation Format: Hitomi Yamashita, Kentaro Nakayama, Noriyoshi Ishikawa, Toshiko Minamoto, Tomoka Ishibashi, Kohei Nakamura, Kaori Sanuki, Ruriko Ono, Masako Ishikawa, Takeshi Isobe, Satoru Kyo. Microsatellite instability is a potential biomarker for immune checkpoint inhibitor in endometrial cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2621. doi:10.1158/1538-7445.AM2017-2621