Abstract 6770: Spatial characterization of immune microenvironment from early onset metastatic colorectal cancer (EOmCRC) showed a dual prognostic role for IDO1 expression
Authors: Nagaraju Raghavendar Thyagaraja , Franczak Jakub , Möhler Markus , Fontana Elisa , Giraut Anne , Dirix Lieve , Casas-Martin Jose , Borelli Beatrice , Lordick Florian , Smith Elizabeth , Tejpar Sabine , Folprecht Gunnar , Barriuso Jorge 
Published: April 2023

Abstract
Background: Epidemiological studies demonstrate that the incidence of CRC in young adults is continually rising in both Europe and the USA. The differences between the spatial distribution of immune related markers (IRM) and their prognostic role in EOmCRC compared to late onset (LOmCRC) remains to be elucidated.
Methods: Forty paraffin embedded formalin fixed unstained sections from patients (pts) diagnosed with either EOmCRC (≤45) or (≥50) LOmCRC, matched for chemotherapy (chx) and molecular features, all with microsatellite stable disease were included. All tissue samples were obtained from pts enrolled in SPECTAcolor (EORTC-40CRC-GITCG) platform trial. The expression of IRM was studied using the GeoMX Digital Spatial Profiler (DSP). Fifty-seven IRMs were used and three morphology markers (MMs) anti-CD45, pan-cytokeratin and SYTO 13. Three 300 μm regions of interest (ROIs) were selected within the core of the tumour and further 3 ROIs within the active margin of the tumour. Each ROI was segmented based on MMs to obtain a tumour microenvironment (TME) and a tumour (T) mask. The analysis used the GeoMX DSP Advanced Analysis Suite software, R and IBM SPSS. Control for multiple comparisons use a false discovery rate (FDR) threshold of 0.05.
Results: Samples from 40 pts were collected; 19 (47.5%) were EOmCRCs; 16 (40%) were female; 23 (57.5%) with pathological stage IV. The majority being, 23 (57.5%) grade ≥ 2, left sided 26 (65%), oxaliplatin based first line chx 23 (57.5%). Ten (25%) were KRAS mutant (mt), 1 (2.5%) NRAS mt and 1 (2.5%) BRAF mt. The median overall (OS) and progression free survival (PFS) for the entire cohort was 36.6 months (m) 95%CI (33.5 - 39.7) and 11.7 m (8.1 - 15.3), respectively.The &lt;0.05 FDR differential expression analysis based on tissue segmentation uncovered 9 hits when comparing the TME between different age groups and 2 hits when comparing T segments, all overexpressed in LOmCRC. Indoleamine 2,3-dioxygenase 1 (IDO1) was differentially overexpressed in TME (adjusted p=0.043) and T (adjusted p=0.042) for LOmCRC.In the EOmCRC group IDO1 relative high expression in T was an independent marker associated with worse survival outcomes after multivariate cox regression corrected for the rest of significant markers (MVCC) for OS, HR: 7.01*105 95%CI (9.08*105-5.41*1010), p=0.003 and PFS, HR:7.7*105 95%CI (1.96-30.3*106), p=0.029. However, interestingly high IDO1 in TME was an independent marker associated with better OS, HR: 0.02 95%CI (0.01-0.46), p=0.015.
Conclusion: Differential expression analysis of IRMs found IDO1 as differentially expressed in both segments (T and TME). Furthermore, high IDO1 expression seemed to have a dual prognostic role depending on the segment analysed, showing worse OS when found in the tumour but better OS when found in tumour microenvironment for early onset mCRC.
Citation Format: Raghavendar Thyagaraja Nagaraju, Jakub Franczak, Markus Möhler, Elisa Fontana, Anne Giraut, Lieve Dirix, Jose Casas-Martin, Beatrice Borelli, Florian Lordick, Elizabeth Smith, Sabine Tejpar, Gunnar Folprecht, Jorge Barriuso. Spatial characterization of immune microenvironment from early onset metastatic colorectal cancer (EOmCRC) showed a dual prognostic role for IDO1 expression. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6770.