Hóa chất có phải là thủ phạm gây ung thư ở người trẻ tuổi? Đây là những gì bằng chứng cho thấy

Cancer is traditionally known as a disease affecting mostly older people.

But some worrying trends show cancer rates in younger people aged under 50 are on the rise.

This week’s ABC 4 Corners suggest chemicals, including plastics, may play a role in rising rates of these early–onset cancers.

So what does the evidence say is causing this increase? And what can we do about it?

Why does cancer mostly affect older people?

Each cell in your body contains a copy of your DNA – the instructions needed to keep that cell functioning properly.

However, DNA can be damaged or “mutated” in such a way that a cell will no longer do the job it’s supposed to.

Some mutations will allow a cell to make too many copies of itself and grow out of control. Others can protect it from dying. And others still allow it to move around and travel to other organs where it doesn’t belong.

Accumulating too many of these DNA mutations can lead to cancer.

Every time a new cell is made in our body, a copy of our DNA is made too. Sometimes, due to random chance, mistakes occur which introduce genetic mutations.

Think of it like making a photocopy of a photocopy, and so on. Each copy will be slightly different than the original.

Most DNA mutations are harmless.

But your cells are making billions of new copies of themselves each day. So the older you get, the more DNA copies you will have made during your lifetime, and the more likely you are to have dangerous mistakes in those copies.

As we get older, our bodies aren’t as good at recognising and removing cells with dangerous mutations. That’s why cancer is much more common in older people.

What’s causing cancer in younger people?

One of the reasons increased cancer rates in younger people is so worrying is it means there are likely environmental factors involved we don’t yet know about.

Environmental factors are anything outside of our bodies: things such as chemicals, viruses and bacteria, the amount we exercise, and the foods we eat.

Many of these environmental factors can increase the likelihood of DNA copying mistakes, or even directly damage our DNA, increasing our risk of cancer.

One well–known example is ultraviolet (UV) radiation from the sun, which can lead to skin cancer. Another is smoking, which can lead to lung cancer.

Fortunately, public awareness campaigns about the dangers of sun exposure, and reduced rates of people smoking cigarettes, have led to falling numbers of skin and lung cancer cases in Australians under 50 over the past 30 years.

But other types of cancer – including cancers of the liver, pancreas, prostate, breast and kidney – are increasing in young people in Australia. The trend is global, particularly among richer, western countries.

What role do chemicals play?

Researchers are working to understand the causes of these increases. Currently, chemicals are in the spotlight as an environmental factor of particular interest.

We’re exposed to more chemicals in the modern day than many of our ancestors were – things such as air pollution, food additives, plastics and many more.

Alcohol and cigarette smoke aside, most chemicals that are definitively linked to cancer are not ones most people would regularly encounter, as they’re restricted to spaces such as industry.

One of the main chemicals of concern are plastics, which are ubiquitous: almost everyone encounters them, every day.

Experts agree plastics represent an overall massive general risk to human health and the environment.

But there are so many thousands and thousands of plastics, it’s hard to point fingers at specific ones causing specific problems, including cancers.

Studies using animals can give strong evidence one way or another. But in humans who are exposed to thousands of different environmental factors every day, it’s difficult to definitively state “risk factor X contributes to cancer Y”.

So, it’s not possible to point to a single “smoking gun” in the case of the increasing early–onset cancer rates.

Let’s use colorectal cancer (also called bowel cancer) as an example to illustrate the issue.

Why are young people getting bowel cancer?

In older people, bowel cancer rates are actually falling. This is thought to be in part due to improved testing and screening helping to catch and destroy dangerous cells before they actually become cancer.

But early–onset bowel cancer rates are rising.

Some people speculate this may be due to increased exposure to plastics, as the digestive system is exposed to these through the food we eat. This includes things such as nano- or micro-plastics, or chemicals leaching out of the plastics into foods, such as PFAS (per– and poly-fluoroalkyl substances) .

But there are other potential culprits, such as diet and lifestyle, with obesity and alcohol intake correlating with increased cancer rates.

Bacteria may also play a role: the types of bacteria found in your microbiome are thought to contribute to bowel cancer risk. Even exposure to certain bacterial toxins has been linked to bowel cancer risk.

How can you reduce your risk of cancer?

While there is no definitive evidence linking chemicals to increased cancer risk in young people, this is an area of intense ongoing research. Reducing your use of and exposure to plastics and chemicals where possible is still probably a healthy thing to do.

On top of that, you can reduce your overall cancer risk through regular exercise and maintaining a healthy, balanced diet.

If you have any concerns, and particularly if you have a family history of cancer, consult your doctor.

Sarah Diepstraten receives funding from Cure Cancer Australia and My Room Children‘s Cancer Charity.

John (Eddie) La Marca receives funding from Cancer Council Victoria. He is affiliated with the Olivia Newton-John Cancer Research Institute and the Walter and Eliza Hall Institute of Medical Research.