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How can cancer kill you?

Many people have questions about how cancer can kill you.

Not all cancers cause death

Firstly, it's important to say that not all cancers kill you. Overall, more than 50% of people diagnosed with cancer live for more than 5 years. Some cancers have survival rates of more than 90%.

Cancer at an early stage does not kill you. So a lot of effort is put into early diagnosis when treatment is likely to work best.

What can happen

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

Digestive system

A cancer that grows in part of the digestive system can block it, or partly block it. So food can't go through the intestines 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 often becomes infected.

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

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


Cancer in the bones can affect the calcium balance of the body. It can cause a lot of calcium to be released into the bloodstream. Normally the body has systems to correct this sort of imbalance. 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 unfortunately the calcium levels will rise in the blood. If calcium continues to go up, it will cause you to become unconscious and eventually die. 

Cancer cells can affect the bone marrow. Eventually you might not have enough healthy bone marrow to make blood cells. You won't have enough oxygen circulating around your body if you don't have enough red blood cells. A drop in white blood cells means you have less resistance to infection. A drop in platelets means you're at greater risk of abnormal bleeding.


The human body has very finely balanced limits of certain body salts and chemicals. A cancer that has spread to the liver or bones can upset this chemical balance. 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. 

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 could 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 unfortunately it can become too much for the body to cope with.

Talking about dying

Although this is a difficult subject for people to talk about (including for some doctors and nurses), it might help you to ask your specialist doctor or nurse about how you or your relative might die.

It's 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.

Many people are relieved to find out that they (or their relative) are likely to become unconscious shortly before they die. What you imagine might happen before death is often far worse than the reality. It's important to remember also that very good pain control is available and no one with cancer should die in pain.

Last reviewed: 
14 Mar 2014
  • Cancer and its management 
    R. Souhami and J. Tobias
    Blackwell Publishing. 2011

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