Colon Cancer in Younger People Has a Very Different Biological Identity From That in Older People
In this article
An Alarming Picture
Why Younger People?
A worrying reality is increasingly common in oncology clinics: colorectal cancer incidence is rising worldwide among people under 50. They now account for 10% of all cases and are often diagnosed at an advanced stage.
But the key question is: "Is cancer in a 50-year-old biologically the same as cancer in a 30-year-old?"
A new, comprehensive study presented at the ASCO Gastrointestinal Cancers Symposium 2026 (Abstract 19) gives a clear "NO." Particularly in the immunotherapy-responsive dMMR/MSI-H subgroup, younger patients’ tumors were shown to have genetic and molecular features entirely different from older patients’. This article explains why treatment planning for younger patients should differ.
Study Scope: A Major Analysis of 3800 Patients
Led by Dr. Michela Bartolini at the University of Southern California, the team examined tumors from 3,846 patients with dMMR/MSI-H features using state-of-the-art NGS DNA/RNA sequencing.
- Younger Group (Early-Onset): 496 patients under 50.
- Older Group (Late-Onset): 3,350 patients over 50.
Who Is at Risk? Younger Patients Have a Different Profile
The study found striking differences in who develops these tumors and where they occur among younger patients.
Younger vs. Older Patient Profiles
Men predominated among younger patients (65%), while the older group was more balanced (40% men).
Hispanic patients were more common in the younger group (13% vs 7%), while White patients predominated in the older group (72%).
In younger patients, tumors more often involved the left colon and rectum (27% and 15%), while right-colon involvement was more common in older patients.
Genetic Fingerprints: Like Two Different Diseases
Perhaps the most important finding is the gap between the tumors' genetic structures. Tumors in younger patients develop through entirely different genetic pathways from those in older patients.
Treatment Implications: What Will Change?
As Dr. Bartolini emphasizes, although these data are currently retrospective, they offer critical clues for treatment selection:
- Immunotherapy Response: Younger patients' tumors are more immunogenic, stimulating the immune system. This suggests they may respond to immunotherapies such as pembrolizumab and nivolumab even better than older patients.
- Second-Line Treatment: What happens after progression on immunotherapy? Younger patients have higher sensitivity scores for targeted drugs such as cetuximab, while different pathways, such as MAPK, are active in older patients. The backup plan should therefore also vary with age.
- Bartolini M, et al. Early-Onset dMMR/MSI-H CRC Exhibits Distinct Clinical and Molecular Features Compared to Late-Onset Disease. ASCO Gastrointestinal Cancers Symposium. 2026; Abstract 19.
- Sinicrope FA. Increasing incidence of early-onset colorectal cancer. N Engl J Med. 2022;386(16):1547-1558.
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