How can cancer kill you?

Many people have questions about how cancer can kill you. It’s something that most people worry about it at some point.

We know that talking about this can be difficult. You can save to read this information another time when you feel ready. And it’s ok if you don’t want to read this information at all.

Not all cancers cause death

Firstly, it's important to say that not all cancers cause death. Overall, half of the people (50%) diagnosed with cancer in England and Wales live for 10 years or more. Cancer survival is improving and has doubled in the last 40 years in the UK.

Cancer at an early stage doesn’t usually kill you. So a lot of effort is put into early diagnosis when treatment is likely to work best.

What happens?

How cancer causes death depends on your cancer type and which parts of your body are affected. Some cancers start in or spread to a part of the body that does something essential for life.

Digestive system

The digestive system is also called the gastrointestinal (GI) system. It includes the:

  • food pipe (oesophagus)
  • stomach
  • pancreas
  • liver
  • small and large bowel
Diagram showing the parts of the digestive system

A cancer that grows in the digestive system can block it, or partly block it. So food can't go through the gut and the nutrients and calories you need can't be absorbed.

You might be able to have surgery to remove the blockage. But if this is not possible, your medical team will do all they can to control your symptoms.

If you can't eat and drink, you are less able to cope with other problems, such as infection.


A cancer might block off part of the lung. This part then collapses and can become infected.

When cancer blocks the lungs, there may eventually be not enough healthy lung tissue to allow you to absorb the oxygen you need.

If you have advanced cancer, you might not have the strength to fight off a lung infection, even with strong antibiotics. So the infection can eventually lead to death.


Cancer in the bones can cause calcium to be released into the bloodstream. This can affect the calcium balance of the body. Normally the body has systems to correct this, but when the imbalance becomes too great the systems don't work any more.

There is treatment to bring calcium levels back to normal, but these only work for a limited time. Then the calcium levels can continue to rise in the blood. High levels of calcium in the body can cause you to become unconscious and eventually die. 

Cancer cells can affect the bone marrow. The bone marrow if a spongy material that fills the bones. It produces very early cells called stem cells which then develop into new blood cells. Eventually, you might not have enough healthy bone marrow to make new:

  • red blood cells to carry oxygen around your body
  • white blood cells to flight infection
  • platelets to stop bleeding


The liver is the chemical factory of the body. It carries out many tasks and is very important in maintaining the balance of body chemicals. A cancer that has spread to the liver can upset this chemical balance.

It can be life threatening if this chemical balance can't be corrected.

Blood vessels

Cancers can grow into and damage blood vessels in a vital part of the body. This can cause bleeding. For example bleeding in the brain is a stroke, which can be fatal if the body can't control it. 


Many treatments can control cancer for a long time, even if they can't cure it. But if a cancer continues to grow, then it can become too much for the body to cope with.

Talking about dying

Talking about dying can be very difficult and people often avoid the subject. Sharing your feelings can help everyone involved to cope better.

Dying is something most people worry about at some point. Talking about the way the cancer is affecting your body can help to lessen at least some of those worries.

What happens in the last days of life is different for everyone. Many people are relieved to find out that they, or their relative, are likely to become unconscious shortly before they die.

Last reviewed: 
16 Dec 2019
  • Cancer and its management 
    R. Souhami and J. Tobias
    Blackwell Publishing. 2011

  • Care of dying adults in the last days of life
    National Institute for Health and Care Excellence (NICE), December 2015

  • Oxford Textbook of palliative medicine (5th edition)
    N Cherny and others
    Oxford University Press, 2015

  • 40-year trends in an index of survival for all cancers combined and survival adjusted for age and sex for each cancer in England and Wales, 1971–2011: a population-based study
    M Quaresma, M Coleman and B Rachet
    The Lancet, 2015. Vol 385, Issue 9974, Pages 1206-1218

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