The impact of the immune microenvironment in patients with GEP-NETs.

Abstract

267 Background: The immune microenvironment in neuroendocrine tumors (NETs) remains largely unexplored with very limited data evaluating its impact on survival. We aimed to characterize the immune microenvironment and lymphocytic infiltrate in patients with gastroenteropancreatic (GEP) NET. Methods: We performed comprehensive immune profiling for CD3, CD8, PD-1, IDO, and PD-L1 expression in two cohorts of patients with primary GEP-NET: patients who had short progression free survival (PFS) ≤ 4 years (n = 12) or long PFS > 4 years (n = 14) following surgical resection. Tumor associated immune infiltrates in the tumor, inner and outer invasive front were recorded and quantified. The percentage of PD-L1 membranous expression was manually counted in tumor, stroma and invasive front. To account for the correlation among multiple samples within the same patient, generalized estimating equations (GEE) were used for model estimation and hypothesis testing. Results: Patients with shorter PFS had larger primary tumor size compared to patients with longer PFS (Wilcoxon p value = 0.02), with no statistically significant differences in Ki-67 expression. For all patients univariate GEE results showed a higher mean expression of CD3+, CD8+, and PD-1+ cells at the interface (inner and outer) as compared to the tumor region: 1.28 (95% CI: 0.98, 1.58, p < 0.0001), 0.99 (95% CI: 0.67, 1.32, p = 0.0005) and 1.38 (95% CI: 0.90, 1.38, p < 0.0001) respectively. Comparison between the two groups showed that tumors from patients with a longer PFS had higher intratumoral CD3+ TILs densities than did those from patients who had a shortened PFS (0.88, 95% CI: 0.44, 1.31, p = 0.004). Intratumoral expression of CD8+TILs, and IDO+ cells tended to be higher in the long PFS group (p = 0.143 and 0.29 respectively). While the probability of positive PD-L1 expression did not differ according to location, it was higher in patients with shortened PFS (odds ratio = 1.96; 95% CI: 0.64, 5.93), though not significant. Conclusions: Higher intratumoral T cell infiltrate (CD3+) is associated with a favorable outcome and longer PFS following resection for GEP-NETs. Immune escape is a potential mechanism for disease progression and warrants further investigation as a therapeutic strategy for this disease.