Global Study Uncovers Why Colorectal Cancer Strikes Young Adults More Often
A landmark 17-country genomic study reveals distinct mutational signatures driving early-onset colorectal cancer, pointing to environmental causes.
Summary
Researchers sequenced colorectal cancers from 11 countries across 17 nations, comparing mutational signatures in early-onset (under 50) versus later-onset cases. They identified geography-specific and age-specific patterns of DNA damage, including a novel mutational signature linked to early-onset disease that resembles damage caused by reactive oxygen species or certain dietary exposures. Tumors from Southeast Asia, South America, and Eastern Europe showed distinct mutational profiles compared to North American and Western European cases. The findings suggest that rising rates of early-onset colorectal cancer may be driven by specific, identifiable environmental or dietary mutagens acting on the colon in younger people, offering new targets for prevention and early detection strategies worldwide.
Detailed Summary
Colorectal cancer (CRC) incidence in adults under 50 has been rising in high-income countries for decades, yet the biological drivers behind this trend remain poorly understood. This landmark multinational study set out to characterize the mutational processes at play in CRC across different geographic regions and age groups, using whole-genome sequencing of tumor-normal pairs from patients enrolled across 11 countries spanning 5 continents.
The research team, led by investigators at UC San Diego, the Wellcome Sanger Institute, and IARC/WHO, performed comprehensive mutational signature analysis on hundreds of CRC genomes. They extracted signatures across single-base substitutions (SBS), doublet-base substitutions (DBS), and small insertions/deletions (ID), then mapped these to known COSMIC signatures and de novo discovered patterns. Special attention was paid to separating tumors by patient age at diagnosis and country of origin.
Several striking findings emerged. A previously poorly characterized mutational signature — tentatively linked to reactive oxygen species or specific dietary mutagens — was significantly enriched in early-onset CRC cases compared to later-onset tumors. This signature was not explained by mismatch repair deficiency or other known hereditary causes, suggesting a distinct environmental exposure disproportionately affecting younger colons. Geographic stratification revealed that tumors from Southeast Asian countries (Thailand) and Latin American cohorts (Brazil, Colombia) harbored mutational profiles distinct from those seen in European and North American samples, implicating region-specific environmental, dietary, or microbiome-related carcinogens.
The study also confirmed and extended prior findings on the role of colibactin — a genotoxin produced by certain gut bacteria — evidenced by a characteristic SBS and ID signature (SBS88/ID18) that appeared at varying frequencies across geographic groups, consistent with differential colonization by colibactin-producing E. coli strains. Defective mismatch repair (MMR) and POLE/POLD1 proofreading signatures were identified at expected frequencies and did not account for the age- or geography-specific patterns.
The implications are significant for cancer prevention and early detection. The identification of geography- and age-specific mutational exposures opens pathways for targeted screening strategies in younger populations and for designing interventional studies aimed at reducing specific carcinogen exposures. Caveats include modest sample sizes from some countries, potential tumor tissue quality variation, and the inherent challenge of attributing signatures to specific causal agents without direct exposure data.
Key Findings
- A novel mutational signature enriched in early-onset CRC (under 50) suggests a distinct environmental or dietary mutagen targeting younger colons.
- Geographic analysis across 17 countries revealed country-specific mutational profiles, implicating region-specific carcinogens including diet and microbiome factors.
- Colibactin-associated signatures (SBS88/ID18) from E. coli varied significantly across geographic cohorts, linking gut microbiome composition to CRC mutagenesis.
- Early-onset CRC mutations were not primarily explained by hereditary MMR deficiency or POLE mutations, pointing to environmental causes.
- Findings provide a genomic basis for the rising incidence of CRC in adults under 50 and highlight targets for prevention.
Methodology
Whole-genome sequencing of matched tumor-normal pairs from CRC patients across 11 countries in 17 geographic cohorts. Mutational signature analysis used both reference COSMIC signatures and de novo extraction across SBS, DBS, and ID mutation classes. Age at diagnosis and geographic origin were used as primary stratification variables.
Study Limitations
Sample sizes from individual countries varied and some cohorts were small, potentially limiting the statistical power of geographic comparisons. Direct exposure or dietary data were not available to causally link signatures to specific agents. Tumor heterogeneity and tissue preservation differences across international sites may introduce technical variability.
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