• Question: what causes cancer?

    Asked by georgie to Gioia, Iain, Jo, Leo, Mariam on 14 Jun 2010 in Categories: . This question was also asked by bubbles1234, abrahams1, batchelor1, wren1, bean9697, blondes, jogliquorandlime, mgrgrl, frank123rous, x9hayley4x, hollynsarah, chazzanmegzoz, sophietify, scwarlett, scienceisababe, annibella13, russarianpantsxx.
    • Photo: Mariam Orme

      Mariam Orme answered on 12 Jun 2010:

      That’s a very good question!

      As you may know, your body is made up of trillions of little units called cells, and each cell has a copy of your DNA in it. Everyone starts out life as one single cell, which grows and divides to make a fully grown human. But even in adults, cells have to keep growing and dividing to replace cells that die (which happens a lot during the natural course of things) and to repair damage, for example if you cut yourself.

      So, what’s that got to do with cancer? Well, cancer is caused by cells that grow and divide too much. This uncontrolled growth happens when the DNA of a cell gets mutations that make it grow more than normal and/or make it stop responding to signals from surrounding cells that would usually tell it to stop growing or to die.

      Now the next obvious question is: how does a cell get these mutations? When a cell divides, it has to replicate its DNA (one cell turns into two, and each one needs a copy of the DNA). During this copying process mistakes sometimes happen, so the DNA gets changed slightly: that’s a mutation. There are ‘proof-reading’ mechanisms to make sure DNA gets copied accurately, but occasionally a mistake slips though. Most mutations are harmless and don’t do any damage, but sometimes they are the sort of harmful mutation that can cause cancer. So, mutations happen naturally, but at a very low rate; however, some things make mutations happen much more frequently – like the chemicals found in cigarettes, or UV radiation from sunlight – and so increase the risk of getting cancer.

      I hope that makes sense and answers your question!

    • Photo: Iain Moal

      Iain Moal answered on 14 Jun 2010:

      Cancer is cause by damaged DNA. There are lots of things which can damage DNA and cause cancer. Sometimes a mistake is made when DNA is copied when cells divide. DNA can also be damaged by certain types of viruses (retroviruses), by ionising radiation (such as UV from the sun, or radiation from radioactive materials) or by carcinogenic chemicals (such as those found in smoke). Eating the wrong types of food can also increase the risk of cancer. Succeptibility to cancer can also be inherited.

      Cancer, however, doesn’t happen because of any signle mutation in the DNA, but by the accumulation of many mutations. That is why the older someone get, the more likely they are of developing cancer, because they have accumulated more mutations.

    • Photo: Gioia Cherubini

      Gioia Cherubini answered on 14 Jun 2010:

      Hi Georgie,

      Imagine the body as a big team formed by millions of cells. To work well, every cell has to be a team player, listening to what the other cells say and adjusting its behaviour depending on what the other cells do. One of the most important things to coordinate is how many times a cell can divide and, when it gets old, to kills itself, because the number of players (the cells) in a body has to be perfectly regulated.
      Now imagine a cell that has gone mad and doesn’t want to play with the others anymore and doesn’t want to respect the rules: that is a cancer cell.
      A cancer cell doesn’t respect anymore the signals that say when to divide and when to kill itself, so not only it divides indefinitely growing as a tumour and invading the body, but also it escapes all the mechanisms to lead to its death.
      The different tumours depend on where the first cell has gone mad, so if the cell was in the skin, then there will be a skin cancer, if in the colon, then it’s colon cancer and so on.

    • Photo: Joanna Watson

      Joanna Watson answered on 14 Jun 2010:

      Hi georgie, bubbles1234 and abrahams1.

      The other scientists have all given really good answers about what causes cancer.

      As epidemiologists, we try to work out what it is that makes the mutations in the DNA more likely to happen. I would definitely agree with Iain, the older you get the more likely you are to have accumulated lots of mutations in your DNA. The other main cause of these mutations is smoking!

      There are lots of other things that can make people more likely to get cancer, like some viruses, radiation and some chemicals – and lots of things cause some cancers but not others. For example, too much time in the sun without sunscreen can make you more likely to get skin cancer, but won’t make you more likely to get bowel cancer.