Cancer as a cause of sickness

This page tells you about how cancer can cause sickness. There is information about

Chemicals made by the cancer
Raised pressure from a brain tumour
Tumours blocking the digestive system
Sickness in advanced cancer

Some types of cancer can make chemicals in your body that affect the way your cells work. Cancers that stop your kidneys and liver working properly can make you feel or be sick.

If you have a brain tumour or a cancer that has spread to your brain, it may cause increased pressure in the head. As the skull is made of bone, there is a fixed amount of space for the brain. The growing tumour increases the pressure inside this fixed space. You may hear this called raised intracranial pressure (raised ICP). The increase in pressure causes

Sickness
Headache
Drowsiness

If your cancer is growing in your digestive system (for example, in your bowel or stomach), it can stop food from passing through. This is a common cause of feeling sick.

Some people in the advanced stages of cancer may feel or be sick a lot. This type of sickness is very different to that of people having chemotherapy or radiotherapy. It can severely affect your day to day life and make you very tired and depressed.

People with advanced cancer can feel and be sick for different reasons. These include

The cancer itself
A blockage in the bowel (bowel obstruction)
Side effects of drugs such as painkillers
Constipation
Too little fluid in your body (dehydration)
Too much calcium in the blood
Slow gut
Kidney or liver problems
Stomach ulcers

As with any symptom, the best thing to do is try to treat the cause. For example, if constipation is causing the sickness, then treating the constipation should control the sickness. Sometimes it isn't possible to treat the cause. In this case, anti sickness drugs are the next best choice.

Too much calcium in the blood

Sometimes cancer can make calcium leak into your bloodstream. This can happen if cancer cells in the bones start to break down the bone cells. But it can also happen because the cancer has upset the body's normal system for controlling calcium levels. Calcium is important for keeping your bones strong and your nerves working properly.

Normally, the body regulates calcium levels very closely. Too much calcium in the blood is called hypercalcaemia. It makes you feel very thirsty, sick, constipated and drowsy. You may also pass a lot of urine as your body tries to get rid of the extra calcium. Confusion and muddled thinking can also be a sign. If hypercalcaemia is not treated, it can make you drowsy and difficult to wake. If it is left untreated, you could eventually become unconscious. There is more about hypercalcaemia in this section of CancerHelp UK.

Slow gut

The digestive system can sometimes slow down due to

Cancer cells in the abdomen pressing on the muscles of the bowel
Cancer cells pressing on the nerves that supply the bowel (the coeliac plexus)

As food does not pass through the bowel as quickly as normal this can make you feel sick. Doctors call this sluggish gut.

Emotional effects

Being very nervous or worried about cancer and its treatment can make you feel sick or even be sick. Sometimes talking about your situation can help to reduce your worry and so reduce sickness.