Why do people have cancer?

This is an article from Curious Kids, a children's series. The Conversation is about asking children to send questions they want an expert to answer. All questions are welcome – serious, weird or crazy! You might also like the Imagine This podcast, a co-production between ABC KIDS Listen and The Conversation, based on Curious Kids.

Why do people have cancer? – Sascha, 8, Hurstbridge, Victoria.

It's a really tough question, Sascha. Many very smart people work hard to try to answer it. I have been working on this problem for many years and, to be honest, I am always amazed at its complexity.

Before talking about Why we have cancer, it helps to understand How we have cancer.

Read more:
Interactive Body Map: What is really giving you cancer?

All living things consist of tiny building blocks called cells. In humans, there are hundreds of different cell types, all with special tasks to accomplish. They build our various organs like our skin, our brain and our bones. Some cells (like the brain and bones) can live for many years, while others (like red blood cells) live only a few weeks.

A human body is made up of thousands of billions of cells, far more than any visible stars in the night sky.

As we grow up, our body needs to make new cells. And as cells age or get damaged, they die and need to be replaced. It helps to keep us healthy.

The simplest way to think about cancer is that sometimes one of these billions of cells starts to get out of control and refuses to die. This uncontrollable cell divides and splits into millions of copies. It can develop to form a tumor or, in some cases, like leukemia, spread through the blood.

Cancer cells can also spread to other parts of our body where they would not normally be found. This can cause important organs to stop doing their job and make us very sick or dying.

Copy the code – and make mistakes

What's really amazing about cells is that they contain the instructions to reproduce. These instructions are stored in a code called the genome, made up of a very nice chemical called DNA.

And if you take the DNA of all the cells of a human being and align it, it would stretch around the moon and vice versa six or seven times.

The cells of the alphabet used to write this DNA code consist of four different chemical "letters": A, C, T, and G. copied exactly each time a cell splits to make a copy of itself. .

To help you understand this incredible feat of biology, imagine trying to copy the complete Harry Potter book series a thousand times in handwriting. That's what a cell has to do every time it splits, and it happens millions of times a day in our body.

You can watch an animation of the incredible and tiny machine used by cells to copy DNA here:

With all this DNA to copy, cells inevitably make spelling errors – we call these errors "mutations". Sometimes these mutations change the meaning of a cell's instruction manual, causing it to lose control and form a tumor.

That's what we call cancer.

But why?

Now back to the question of Why we have cancer.

Different scientists argue a little bit about this issue, but this seems to boil down to a combination of bad luck and various experiences you may have in life. Things like excessive sunlight, some chemicals (such as tobacco smoke), alcohol, certain foods and even some viruses can increase our chances of mutating in our DNA.

Because these mutations in DNA take a long time to accumulate, cancer is most often seen in the elderly. Children sometimes have cancer, but fortunately it is relatively rare. In general, the evolution would mean that few people would be suffering from a disease as horrible as cancer. But since most people get cancer after their children, the evolution is almost blind to cancer. People who may be at higher risk of cancer because of their genes live long enough to pass it on to their children.

You can reduce your cancer risk by making healthy and sensible life decisions, but you can not prevent them completely. Unfortunately, as I said earlier, it's at least partly due to bad luck.

Importantly, we can almost never say for sure why a person has cancer.

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