This entry is part 2 of 23 in the series Science Surgery

Our Science Surgery series answers your cancer science questions.

If you have a question that you’d like us to answer, send it to us using the email address at the bottom of this post.

Patrick asked: ‘What factors lead to a cell becoming cancerous?’

This question can be answered in two words: faulty genes. But what does that really mean?

Our bodies are made of cells, each with different jobs. Some help store our memories, others allow us to swallow our food. This range of different jobs is made possible by the incredibly long strands of DNA each cell holds. That DNA carries the instructions a cell needs to do its job, grow and survive.

Those instructions are tightly controlled so that cells only do what they’re supposed to, when they’re supposed to do it. And it’s these controls that keep us healthy. But if there is a mistake in the instructions, then things can start to go awry.

The DNA double helix

Faults in DNA can make cells grow out of control

Imagine someone following a ticket machine to make coffee orders. If the ticket machine develops a fault and starts churning out too many tickets, the barista will start making excessive amounts of coffee. In this scenario the ticket machine is our DNA, and the ticket is a signal telling the cell to grow.

Just as making coffee is the barista’s job, so cells can make growth signals as part of their normal role, but making too many can result in chaos. With all these excess signals, cell growth can become out of control and eventually result in the formation of a tumour.

In the coffee shop it would make sense to have an emergency repair kit to fix the faulty ticket machine. Our cells are equipped with exactly that too. They carry molecules that work as tools to fix mistakes in DNA as they arise.

But these tools aren’t fool proof, and sometimes mistakes don’t get fixed. On top of that, some cancers are caused by mistakes in the tools themselves, such as those caused by faulty BRCA1 and BRCA2 genes. This leads to more and more genetic faults building up inside cells over time, increasing the chance that eventually a cell will turn cancerous.

That brings us to another important factor in the development of a cancerous cell: accumulation of damage to DNA. One tiny DNA mistake wouldn’t be enough for the cell to become cancerous, just like one rogue coffee ticket wouldn’t lead to carnage in a well-run café. It’s the steady build-up of damage to a cell’s DNA that might ultimately push it over the edge, causing a tumour to form when the cell grows uncontrollably.

Location, location, location

So where do these faults come from in the first place?

They can happen in two main ways.

Firstly, the way we live our lives, such as choosing to smoke or drink alcohol, can damage our DNA. These effects are combined with certain things in our environment we can’t control, such as pollution, which also contain harmful chemicals that damage DNA.

But secondly, faults in DNA can also arise naturally.

When a cell makes a copy of itself, for example in the bowel lining to replace cells that are lost when food passes through, it has to make an exact duplication of its DNA. The DNA is made up of billions of chemical ‘letters’ all strung together, so there is a chance that mistakes in the copying process are made along the way. Imagine trying to type out the dictionary without making a typo.

In the same way our computers and smartphones slow down over time, as you get older your cells become tired too. The tools a cell uses to avoid DNA faults don’t work as well as they used to, meaning mistakes are more likely to appear.

But to add another factor into the mix, it’s not just the faults themselves that are important, it’s also where they crop up in the DNA code.

Not every cell in our body needs to replicate itself. This is only necessary as we grow up and get bigger, or through fixing the normal ‘wear and tear’ processes of life, such as healing cuts and grazes. And it’s only the cells that are capable of dividing that can go on to form a tumour. A faulty gene occurring in a cell that can’t copy itself won’t be passed on to other cells.

Similarly, in order for a faulty gene to be passed on through families, then it needs to be present in sperm and egg cells that can develop into a child.

The lowdown

The take home message is that there are lots of things that can turn a cell cancerous, from mistakes that occur naturally to factors we can avoid like smoking. But it’s this crucial set of ingredients, all of which have to combine inside cells, that causes cancer:

  1. A cell that’s capable of dividing
  2. An accumulation of genetic mistakes in this cell
  3. A faulty gene, or genes, resulting from these mistakes
  4. Uncontrolled cell division as a consequence of this faulty gene(s)

It’s possible that as scientists learn more about cancer biology, a wider set of rules will begin to emerge. But it’s through studying these events that scientists will figure out new ways to tackle all cancers, which we urgently need.


We’d like to thank Patrick for asking us this question. If you’d like to ask us something, email [email protected], leaving your first name and location (optional).