e14577 Background: In recent years, immune checkpoint inhibitors have attracted attention and a lot of studies on PD-L1 (Programmed death-ligand 1) have been reported, but their anti-tumor effects are limited to colorectal cancer in which the expression of PD-L1 is infrequent. On the other hand, radiation therapy has been suggested to be closely related to the antitumor effect derived from the immune response. So we report the histological and clinicopathological examination about the relationship between the expression of PD-L1 and CD8 and irradiation in rectal cancer cases in which operation was performed after preoperative chemoradiotherapy (neoadjuvant chemoradiotherapy, NACRT) to clarify the indication for immune checkpoint inhibitors. Methods: Immunohistochemical staining of PD-L1, CD8 as immune related factors was performed on 34 cases in which operation was performed after NACRT(UFT/LV:300mg/m2/day and 75mg/body/day, respectively +RT(45Gy)) was done for locally advanced rectal cancer from January 2005 to December 2014, and we evaluated their preoperative biopsy specimens and resected specimens to examine the relationship between their evaluations and clinicopathological factors. Results: The 5-year survival rate and relapse-free survival rate of 34 patients were 84.4% and 65.5%, respectively, and there were 4 pathological CR cases. In 30 patients excluding CR cases, the expression of PD-L1 in tumor cells was enhanced or emerged in 5 cases(16.7%) and the infiltration of CD8+TIL(tumor infiltrating lymphocyte) was also enhanced in 13 cases(43.7%) after NACRT. Also, patients with PD-L1 expression had significantly poor prognosis (p = 0.0023) than others, and the prognosis tended to be further poor in CD8+TIL noninvasive cases. Conclusions: NACRT for locally advanced rectal cancer induced PD-L1 expression in tumor cells and also induced the infiltration of CD8+TIL.
Neoadjuvant chemoradiotherapy in rectal cancer
