The Gut’s Secret Fingerprints: Why Is Colon Cancer Rising in Young People?
Featured paper: Geographic and age variations in mutational processes in colorectal cancer
Disclaimer: This content was generated by NotebookLM and has been reviewed for accuracy by Dr. Tram.
For decades, we thought of colorectal cancer as an “old person’s disease.” But recently, something strange and worrying has been happening. In the last 20 years, the number of people under the age of 50 getting colon cancer has doubled in many countries. Doctors and scientists have been scratching their heads, trying to figure out why.
A massive new study published in the journal Nature by an international team of researchers—including experts from the University of California San Diego and the International Agency for Research on Cancer—may have finally found a major clue. By looking at the DNA “fingerprints” left behind in tumors, they’ve discovered that a specific type of gut bacteria might be giving some people a “head start” on cancer early in life.
DNA as a Diary: What Are Mutational Signatures?
To understand this discovery, you first have to understand that our DNA is like a diary. Everything we are exposed to—the food we eat, the chemicals in the air, or the bacteria in our bodies—can leave a mark on our genetic code. These marks are called mutational signatures.
Think of it like footprints in the snow. If you see a heavy boot print, you know a human walked there. If you see a small, three-toed print, you know it was a bird. Scientists can now look at a cancer tumor’s genome and see these “footprints” to figure out what caused the cancer in the first place. This new field of study is called “mutational epidemiology”.
The Villain in the Gut: Colibactin
In this study, researchers looked at the genomes of 981 colorectal cancers from 11 different countries, including Canada, Brazil, Japan, and Thailand. They found something startling: many of the tumors contained a specific signature called SBS88 and ID18.
These signatures are caused by colibactin, a toxin produced by certain types of E. coli bacteria in the gut. While most E. coli are harmless, the ones that carry a specific set of genes (called the pks pathogenicity island) produce this “genotoxin” that literally breaks and mutates our DNA.
The study found that these colibactin signatures were 3.3 times more common in people diagnosed with colon cancer before the age of 40 compared to people over the age of 70. This suggests that being exposed to these bacteria early in life might be a key reason why younger people are getting sick.
A Global Mystery: Different Countries, Different Signatures
One of the most fascinating parts of the research was how the cancer “footprints” changed depending on where a person lived. The team found that levels of mutagenic exposure varied wildly around the world.
- Argentina: Tumors here showed high levels of three specific signatures (SBS89, DBS8, and ID_J) that aren’t well understood yet.
- Colombia: Patients here had unique signatures (SBS94 and SBS_F) that were much more common than in other countries.
- Thailand and Iran: These countries generally had lower rates of certain types of DNA damage.
While scientists don’t yet know exactly what causes these specific “local” signatures, they believe they are likely caused by environmental factors or lifestyle habits unique to those regions, such as specific diets or local types of bacteria. Interestingly, the colibactin signatures (SBS88 and ID18) were much more common in countries that have higher overall rates of colorectal cancer.
The “Head Start” Theory
Why does exposure to a bacterium matter so much for a young person? The researchers found that colibactin damage is an “early event”. This means the bacteria likely strike when a person is still a child or a young adult.
Our bodies have “gatekeeper” genes that prevent cancer from growing. One of the most important is called APC. The study found that colibactin is responsible for about 25% of the major mutations in the APC gene in cases where the bacteria were present.
Normally, it takes decades for enough random DNA mistakes to pile up and cause a tumor. However, if colibactin damages your APC gene when you are only 10 or 20 years old, it gives the cancer a massive “head start”. It’s like starting a race halfway to the finish line; you’re going to reach the end much sooner than everyone else. This “early-life mutation burst” could explain why someone in their 30s might develop a cancer that usually doesn’t show up until someone is in their 70s.
Why You Might Not Have the Bacteria Anymore
You might wonder: If bacteria caused my cancer, can’t the doctors just find the bacteria in my gut?
Actually, it’s not that simple. The researchers looked for the bacteria in the tumor samples but often couldn’t find them. They believe this is because our microbiome (the collection of bacteria in our gut) changes over time. You might have the “bad” bacteria when you are 12, they do their damage to your DNA, and then they disappear by the time you are 35. Even though the bacteria are gone, the permanent scars they left on your DNA remain, eventually leading to cancer years later.
What This Means for the Future
This study is a game-changer for how we think about preventing cancer. If we can prove that these bacteria are the primary cause of early-onset colon cancer, we might be able to:
- Screen kids and young adults: We could test people for pks+ bacteria early in life.
- Eliminate the threat: If someone has the dangerous bacteria, we might be able to use specific treatments or probiotics to remove them before they can damage the DNA.
- Better prevention: Understanding that the “seeds” of cancer are sown in childhood means we can focus more on early-life health and nutrition.
The Bottom Line
The rise of colon cancer in young people is a complex puzzle, and this study provides a huge piece of the solution. It highlights that the microbiome in our large intestine isn’t just helping us digest food—it can act as a powerful factor in our long-term health.
While we still have a lot to learn about the “unknown” signatures found in places like Argentina and Colombia, one thing is clear: the fight against cancer starts much earlier than we ever realized. By protecting our DNA from bacterial damage when we are young, we might be able to stop colon cancer before it ever has a chance to start.