Abstract 3574: Cancer testis antigen expression correlates with stromal natural killer cell activation and longer overall survival in small bowel neuroendocrine tumors
Authors: Ayabe Reed I. , Seo Yongwoo D. , Melendez Brenda , Lazcano Rossana , Fields Brittany C. , Wani Khalida , Johnson Sarah , Chelvanambi Manoj , Hudgens Courtney , Hernandez Sharia D. , Ajami Nadim J. , Wargo Jennifer A. , Lazar Alexander J. , Halperin Daniel M. , Estrella Jeannelyn S. , Maxwell Jessica E. 
Published: March 2024

Background: Patients with small bowel neuroendocrine tumors (SBNET) frequently present with metastatic disease and the efficacy of available therapies, including immune checkpoint blockade (ICB), is limited. Toward developing novel immunomodulatory strategies, we interrogated the tumor immune microenvironment of SBNETs using bulk transcriptional and digital spatial profiling (DSP).

Methods: Patients with SBNET who underwent resection at MD Anderson Cancer Center from 2003-2016 were retrospectively analyzed. Overall survival (OS) was assessed using the Kaplan-Meier method and the Cox proportional hazards model was used for multivariate analysis (MVA). Bulk transcriptional profiling was performed using the Nanostring PanCancer-Immune Panel. DSP with whole human transcriptome was performed using PanCK to segment tumor and adjacent stroma; 88 distinct regions were analyzed using differential gene expression and Reactome pathway enrichment pipelines.

Results: Resected SBNET from 42 patients were selected for transcriptional analysis. Unsupervised clustering of gene expression demonstrated dichotomization into high and low cancer testis antigen (CTA) expression. CTA-high patients (n=12) demonstrated elevated expression of type-I interferons (IFN), and CTAs such as PRAME, GAGE1 and MAGEA3 and had significantly longer OS compared to CTA-low patients (n=30; median OS not reached vs 1975 days, p=0.008). MVA controlling for age, sex, stage, and Ki-67% confirmed CTA-high status as an independent predictor of longer OS (hazard ratio [HR] 0.2, 95% confidence interval [CI] 0.05-0.83, p=0.014). A pilot DSP experiment on 4 CTA-high and 4 CTA-low tumors confirmed differential gene expression in the PanCK+ tumor compartment of these samples (R2=0.09, p=0.001). In particular, epigenetic modification genes (e.g., H2BC8, H4C8, H3C1, p&lt;0.001) and epigenetic pathways (e.g., DNA methylation, histone acetylation) were enriched in CTA-high tumors. CTA-high tumors exhibited increased M2 macrophage presence (p=0.025) and increased NK cell activation within the PanCK- stromal compartment (p=0.001).

Conclusions: High CTA and type-I IFN expression in resected SBNET identifies patients with longer survival, agnostic of stage or grade. While CTA expression has been implicated in tumor immunogenicity, this is the first work to identify a clinically relevant signal in SBNET. Increased IFN in CTA-high tumors, corroborated by increased stromal NK cell activation, suggests that enhanced immunogenicity may drive this survival difference. Spatial transcriptomic analysis reveals epigenetic differences in CTA-high tumors and highlights the potential for combination epigenetic modifiers and immunotherapy in future trials.

Citation Format: Reed I. Ayabe, Yongwoo D. Seo, Brenda Melendez, Rossana Lazcano, Brittany C. Fields, Khalida Wani, Sarah Johnson, Manoj Chelvanambi, Courtney Hudgens, Sharia D. Hernandez, Nadim J. Ajami, Jennifer A. Wargo, Alexander J. Lazar, Daniel M. Halperin, Jeannelyn S. Estrella, Jessica E. Maxwell. Cancer testis antigen expression correlates with stromal natural killer cell activation and longer overall survival in small bowel neuroendocrine tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3574.