In recent years, doctors in the United States have been witnessing a troubling trend — colorectal cancer is increasing among people under 50. This shift has raised serious concerns because colorectal cancer has long been viewed as a disease of older adults. Now a new study from the Yale School of Public Health (YSPH) may help explain what makes cancers in younger patients different, and why the numbers continue to climb.
Published in Free Radical Biology and Medicine, the study presents the first comprehensive metabolic comparison between early-onset and late-onset colorectal cancer using matched tumor and normal tissues. The findings suggest that tumors developing in younger adults may grow through unique biological pathways, making them distinct from those seen in older individuals.
What Is Colorectal Cancer?
Colorectal cancer begins in the colon (large intestine) or the rectum, the final parts of the digestive system. These regions help absorb water and store waste before it leaves the body. Sometimes small growths called polyps form in the lining of the colon or rectum. Most polyps are harmless, but some can slowly turn into cancer over several years. When the cells in these growths start multiplying abnormally and uncontrollably, they can develop into colorectal cancer. Early detection is crucial because colorectal cancer often shows few or no symptoms in its early stages.
Younger Tumors Show Different Biology
One of the most striking findings of the Yale study is that early-onset tumors appear biologically different from those found in older adults. According to Dr. Oladimeji Aladelokun, a postdoctoral associate at YSPH, the metabolic patterns in younger tumors show “a different biology,” suggesting that the cancer may be triggered and progress through different chemical processes.
Factors Behind the Rise
Colorectal cancer remains the third most commonly diagnosed cancer and one of the leading causes of cancer deaths in the U.S. But the steady rise among young adults is especially worrying. Cases in people aged 20–39 have been increasing by about 2% every year since the mid-1990s.
Experts believe several factors may be contributing to this surge:
- Rising rates of obesity
- Increased alcohol consumption
- Sedentary lifestyle
- High intake of ultra-processed foods
- Possible disruptions in gut bacteria
- Genetic predispositions
These factors may interact in complex ways, making younger adults more vulnerable than previously understood.
Key Metabolic Discoveries
The Yale researchers analyzed frozen tumor samples collected from 1991 to 2001 and identified 91 metabolites that differed significantly between normal and cancerous tissues. But one molecule stood out: homovanillic acid, which is produced when dopamine breaks down, was uniquely reduced in early-onset tumors. This suggests a possible link between dopamine metabolism and colorectal cancer in younger patients.
Another major discovery was that early-onset tumors had lower levels of PD-L1, a protein often targeted in immunotherapy treatments. Lower PD-L1 may mean that these tumors create a more immunosuppressive environment, potentially affecting how well young patients respond to treatment.
What Happens Next?
Dr. Caroline Johnson’s team is now expanding the research by collecting more samples and exploring whether these metabolic changes can be detected in blood tests, which would make screening easier. If confirmed, these findings could transform how colorectal cancer is screened, diagnosed, and treated in younger adults — a group facing a rapidly growing risk.
