628 Background: A plethora of studies report abundant expression of programmed death-ligand 1 (PD-L1) on tumors to be associated with poor outcome in several cancer forms, whereas immune cell-specific expression of PD-L1 has been associated with improved prognosis in colorectal cancer. However, none of these studies have investigated the association with prognosis according to primary tumor location. This study aimed to investigate the clinicopathological correlates and prognostic impact of PD-L1 and its receptor PD-1 in colorectal cancer, with particular reference to the anatomical subsite of the primary tumor. Methods: Immunohistochemical expression of PD-L1 and PD-1 was analysed in tissue microarrays with tumors from 557 incident cases of CRC from a prospective population-based cohort. Kaplan-Meier and Cox regression analyses were applied to determine the impact of biomarker expression on 5-year overall survival (OS), in the entire cohort and in subgroup analysis of right colon, left colon, and rectum. Results: High PD-L1 expression on tumor-infiltrating immune cells correlated significantly with an improved 5-year OS in univariable and multivariable analysis, adjusted for age, sex, TNM stage, differentiation grade, and vascular invasion, in the full cohort (HR = 0.49; 95 % CI 0.35-0.68), and in primary tumors of the right (HR = 0.43; 95 % CI 0.25-0.74) and the left colon (HR = 0.28; 95 % CI 0.13-0.61), but not in rectal cancer. High tumor-specific PD-L1-expression was not significantly associated with prognosis in neither the full cohort nor according to primary tumor location. High expression of PD-1 on tumor-infiltrating immune cells was significantly associated with an improved 5-year overall survival in the entire cohort (HR = 0.42; 95 % CI 0.21-0.87), but not in subsite analysis according to primary tumor location. Conclusions: This study is, to the best of our knowledge, the first to investigate the prognostic impact of PD-L1 and PD-1 expression according to primary tumor site in colorectal cancer. Dense infiltration of PD-L1+ immune cells was found to be an independent favorable prognostic factor in primary tumors of the right and left colon, but not in the rectum.
Prognostic impact of primary tumor location in metastatic colorectal cancer (mCRC). A 5 year retrospective analysis of our treated population.
