Correlation of cancer testis antigen and interleukin expression with survival in small bowel neuroendocrine tumors.

Abstract

e16247 Background: Patients with small bowel neuroendocrine tumors (SBNETs) frequently present with metastatic disease, and unfortunately, the range and efficacy of available therapies is limited. Immunotherapeutic checkpoint inhibitors have demonstrated benefit in other malignancies and may also play a role in SBNETs, although relatively little is known about the immune infiltrate in these tumors. Toward a goal of developing novel immunomodulatory strategies, we sought to evaluate the tumor immune microenvironment of SBNETs utilizing Nanostring transcriptional profiling. Methods: Patients with SBNETs who underwent surgical resection at MD Anderson Cancer Center from 2003 to 2016 were retrospectively analyzed. Clinicopathologic data was collected, and patients were stratified by survival. Overall survival (OS) from date of resection was assessed using the Kaplan-Meier method, and p-values were calculated using the log-rank test. Multivariate (MV) analysis was performed using the Cox proportional hazards model. Transcription expression from bulk RNA was analyzed using the Nanostring PanCancer Immune Profiling Panel. Results: Resected SBNETs from 45 patients were selected for transcriptional analysis. Unsupervised clustering of RNA expression data revealed separation into high and low expression groups in two distinct transcription panels: cancer testis antigens (CTA) and interleukins (IL). All patients in the IL-high group also were in the CTA-high group. CTA-high patients (n=13) had significantly improved overall survival compared to CTA-low patients (n=32; median OS not reached vs 1975 days, p=0.0032). MV analysis controlling for age, gender, metastatic disease and history of carcinoid syndrome confirmed CTA-high status as an independent predictor of improved OS (hazard ratio 6.6, 95% confidence interval 1.7-26.4, p=0.008). CTA-high patients had significantly elevated expression of CTAs (such as PRAME and GAGE1) and cytokines (such as IL2 and CXCR1). High normalized expression levels of these single genes were independent predictors of improved OS in MV analysis (PRAME p=0.008, GAGE1 p=0.006, IL2 p=0.008, CXCR1 p<0.0001). Conclusions: High expression of CTA and IL signatures in resected SBNETs identified patients with improved survival agnostic of stage. While CTA expression across multiple tumor subtypes have been implicated in their immunogenicity and potential for therapeutic targeting, this is the first work to identify a clinically relevant signal in SBNET. The concurrent increase of key cytokines (which are known to mediate anti-tumor activity) among CTA-high patients suggests an immune-mediated component to their improved survival. Further work is underway to elucidate the epigenetic mechanisms of CTA expression and silencing, with the goal of validating key CTAs such as PRAME and GAGE1 as predictive and therapeutic targets for immunologic intervention.