• Question: Why does cancer keep coming back once you have got rid of it?

    Asked by icedancer to Gioia, Iain, Jo, Leo, Mariam on 16 Jun 2010 in Categories: . This question was also asked by 07tmellor, mychemicalromance, larryandharry, emmaandizzy, stephabel, spunter2010.
    • Photo: Gioia Cherubini

      Gioia Cherubini answered on 16 Jun 2010:

      Well, it is not exactly that it keeps coming back, it’s just that we didn’t manage to get rid of it in the first place most likely. Even if you leave only one cancer cell in the body, it would be capable of growing a new tumour 🙁

    • Photo: Iain Moal

      Iain Moal answered on 16 Jun 2010:

      This is because there are millions of cancer cells in a tumour, and to be fully free of cancer they all need to die. Also, cancer cells can break away from the primary tumour, and start secondary tumours. Of course, surgery of radiotherapy aimed at the primary tumour won’t affect the secondary tumours.

      One interesting idea, which has seen lots of evidence recently, is the idea of cancer stem cells. These are cells which are very different from the other cancer cells. They divide very slowly, so aren’t killed by drugs that target rapidly dividing cells. However, when they divide, one of the daughter cells is a cancer stem cell, and the other is a rapidly-dividing cancer cell which can start a new tumour all over again. So, many chemotherapies designed to kill the bulk of the tumour don’t kill a small number of cells which can start new tumours once the people stop taking the drugs.

      One of the most exciting areas of cancer research at the moment is the idea of targeting and killing cancer stem cells. I think there will be clinical trials into drugs that do this in the near future, and I believe there is good reason to think that this could be a major breakthrough in treating cancer.

    • Photo: Mariam Orme

      Mariam Orme answered on 16 Jun 2010:

      The main reason cancer sometimes comes back is that it’s hard to get rid of ALL of it. For a lot of tumours, doctors can operate to remove most of it, and then the patient will be treated with chemotherapy or radiotherapy to try and kill any cancer cells that were left behind, or that had moved away to another part of the body (that’s called metastasis). But sometimes a few cells survive, and they will keep on dividing to form another tumour, so the cancer comes back.

    • Photo: Joanna Watson

      Joanna Watson answered on 16 Jun 2010:

      If all of the cancer cells are completely gone then you are no more likely to have another cancer than someone else. The treatments that we have aren’t perfect though, so if there are a few cancers cells left behind that the treatment didn’t get rid of they might be able to start growing again and the cancer will come back.

    • Photo: Leo Garcia

      Leo Garcia answered on 16 Jun 2010:

      There are a couple of reasons why this might happen. Firstly, malignant tumours can spread to other parts of the body, in a process known as metastasis. So it might be the case that when the primary tumour is removed (that is, the place where the metastasis spread from), that cancer cells exist elsewhere in the body, and may go on to form other ‘secondary’ tumours.

      Another reason is that it only takes one remaining cancer cell to begin the process of forming another tumour. So, in any treatment, we have to be very sure that all of the tumour is removed.

      Remember that plenty of people are successfully treated for their cancer and they go on to live without it the rest of their lives. As treatment methods have improved, the mortality rate (the number of people dying of cancer) in the UK has decreased over time!

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