P65. Single-Cell Dissection of Early-Onset Colorectal Cancer Reveals Targetable Immunosuppressive and Oxidative Stress Pathways

Introduction: Early-Onset Colorectal Cancer (EOCRC) has rapidly emerged as a major public health concern, with incidence rates rising by 1-4% yearly.This year EOCRC became the leading cause of cancer-related mortality in young Americans, yet the etiology and unique characteristics responsible for its aggressive biologic features remain unclear. 


Methods: Single-cell transcriptomic data of tumors resected from untreated patients diagnosed with microsatellite-stable (MSS) colorectal cancer (CRC) were analyzed. Patients were stratified based on age into EOCRC ( < 50 years) and Late-Onset CRC (LOCRC, ≥ 50 years). Tumor cell composition and gene expression data were investigated to identify differences in the tumor microenvironment (TME) between EOCRC and LOCRC. Results were validated at scale with RNA from the TCGA-COAD project.


Results: Compositional landscape analysis revealed no significant differences between the TME of EOCRC (n = 27) and LOCRC (n = 91). Restricting the LOCRC group to patients aged over 65 (n = 41) revealed a significant enrichment of metaplastic cells in EOCRC. EOCRC tumors demonstrated broad immune dysfunction, with gene set enrichment analysis (GSEA) showing impaired lymphocytic activation and differentiation, immunoglobulin production, antigen presentation, and leukocyte chemotaxis relative to LOCRC. Immune cell interactions were also reduced in EOCRC tumors, accompanied by significant upregulation of immunosuppressive signaling pathways involving macrophage migration inhibitory factor (MIF) and annexin A1 (ANXA1; Fig. 1). In epithelial cells, EOCRC showed increased activity of the Myc pathway, oxidative phosphorylation, and peptidylprolyl isomerase A (PPIA) signaling - programs linked to oxidative stress exposure, tumor progression, and immune suppression. These findings were validated in the TCGA-COAD cohort (n = 466), where GSEA confirmed significant downregulation of immune pathways in early versus late-onset tumors. 


Conclusions: This study is the largest multi-population analysis to date characterizing the TME of EOCRC. Leveraging single-cell transcriptomic data enabled granular dissection of composition and functional states, revealing an impaired immune landscape as a mechanistic basis for the accelerated tumor progression observed in young patients. These analyses uncovered distinct oxidative stress-associated and immunosuppressive pathways uniquely enriched in EOCRC, highlighting potential targets for precision immunotherapeutic strategies that differ from those relevant in LOCRC.