Association of genetic variations within the PD-L2 immune checkpoint gene with outcome in stage II and III colon cancer.

Abstract

626 Background: Immune checkpoints can either inhibit or stimulate T-cell responses and therefore play a key role in maintaining an equilibrium between self tolerance and autoimmunity. Targeting immune checkpoint molecules can result in increased antitumor immunity by stimulation of the immune system. We hypothesize, that variations in genes encoding for both inhibitory or stimulatory immune checkpoint proteins may predict outcome in stage II and III colon cancer patients. Methods: The impact of 6 functional single nucleotide polymorphisms (SNPs) within the PD1, PD-L1, PD-L2, TIM3, OX40 and CD27 genes on time to recurrence was evaluated in 201 patients with stage II and III colon cancer. Genomic DNA was extracted from formalin-fixed paraffin embedded tissue and the SNPs were analyzed by PCR-based direct sequencing. Results: Baseline characteristics were as follows: female/male ratio = 42.8% / 57.2%; median age = 70y (19-91); median follow-up = 43months. The PD-L2 rs16923189 SNP showed significant association with recurrence rate. Patients with a G/G genotype had a higher 3-years recurrence rate compared to those harboring any A allele (41% vs 19%) in both univariate (HR 2.68, 95% Confidence interval (CI) 1.28-5.61, p = 0.006) and multivariate analyses (HR 3.13, 95% CI 1.42-6.28, p = 0.003). The high recurrence rate was most evident among patients with stage III and left-sided tumors carrying the G/G genotype (53% vs 24% and 65% vs 18%) in both univariate (HR 2.87, 95% CI 1.24-6.66, p = 0.009 and HR 5.28, 95% CI 2.24-12.44, p < 0.0001) and multivariate analyses (HR 4.32, 95% CI 1.76-9.91, p = 0.001 and HR 5.20, 95% CI 2.02-12.75, p = 0.001). Conclusions: Our results provide the first evidence, that polymorphisms within the PD-L2 gene might serve as prognostic markers in patients with stage II and III colon cancer. Interestingly, the prognostic effect is most significant among patients with stage III and left-sided colon cancers. Targeting PD-L2 might be a promising approach to further optimize treatment options and to improve outcome of colon cancer patients in the adjuvant setting.