LAUSR

Background: Programmed cell death 1 (PD-1) and its ligand (PD-L1) are key suppressors of the cytotoxic immune response. PD-L1 expression on tumor cells may be induced by the immune microenvironment, resulting in immune escape, and an adverse prognosis in many malignancies. In colorectal carcinoma the response to PD-1/PD-L1 inhibition is correlated with microsatellite instability. However, little is known about the clinicopathologic, molecular, and prognostic characteristics of colorectal carcinoma with PD-L1 expression. In surgically resected colorectal adenocarcinoma, micrometastasis should be crucial for recurrence, and micrometastasis may be related to PD-L1. The aim of this study is to assess the PD-L1 expression and its association with clinicopathologic manifestations. Methods: PD-L1 expression was evaluated in 176 resected colorectal adenocarcinomas using tissue microarrays. Immunohistochemical staining was performed to evaluate the expression of PD-L1. The relationship of clinicopathologic manifestations and PD-L1 expression in colorectal cancer were evaluated by chi-squared test, Kaplan-Meier survival and Cox regression test. Results: High PD-L1 expression was present in 52.8% colorectal adenocarcinoma and was not related pathologic T or N stage. High PD-L1 expression was associated with decreased recurrence rate (p Conclusion: High PD-L1 expression is an independent prognostic factor, such as pathologic stage in colorectal adenocarcinoma. PD-L1 expression is independent prognostic factor, relating immune response to micrometastasis and immune suppression by PD-L1 may not be effective in micrometastasis of colorectal adenocarcinoma. Key words: PD-L1, colon, cancer, immunology, micrometastasis Citation Format: Ilseon Hwang, Keon Uk Park, Jin Young Kim, Hun-Mo Ryoo, Yun-Han Lee. Programmed cell death ligand 1 expression in resected colorectal adenocarcinomas: association with micrometastasis [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 3927. doi:10.1158/1538-7445.AM2017-3927