• Question: when cancer spreads why is it so hard to cure?

    Asked by anon-181865 on 13 Jun 2018. This question was also asked by anon-182023.
    • Photo: Alex Haragan

      Alex Haragan answered on 13 Jun 2018:

      There are quite a few reasons for this.
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      When cancer is small and in one place, it means it is more likely you can chop it all out with surgery. Unfortunately this means also taking away some surrounding normal parts of the body to make sure you have it all. When the cancer gets big sometimes the operation becomes almost impossible as it has grown into surrounding organs.
      Other “directed” treatments like radiotherapy involve directing beams of radiation at the cancer to kill it – when it is in one or two places, it is relatively easily to target. Unfortunately radiotherapy also goes through normal parts of the body and damages them – so again if it is too big or has spread it becomes a limited treatment option.
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      Cancer can spread by several means – it can simply grow directly into surrounding tissue, it can spread through the blood, or the lymphatic system (essentially the waste for your cells), it can spread down empty spaces (for example, along your gut), even along nerves!
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      Once it has spread, or metastasised, it is often in multiple different areas. Often cancers can spread to dozens or more places. And once cancer has started metastasising like this, in theory it only takes one cancer cell for it to start up somewhere else.
      This means surgery and radiotherapy are almost impossible to target all the spreads.
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      This leaves us with treatment that gets around your body via your blood supply, or systemic treatment. Traditionally this involved only chemotherapy – but this also damages a lot of normal cells. More recently we have drugs that are targeted more specifically at just cancer cells, or, as in my work, at getting the immune system to kill the cancer.
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      Even when it looks like all the cancer has gone – it only takes that one cell for it to come back – so it can be tricky! And most of the time we can’t get rid of it all when it has spread to many places – but we are getting new medicines and we are getting better at it.

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