Cancer as a cause of sickness

Cancer itself could cause you to feel or be sick. There are many different reasons why.

These include:

  • chemicals made by the cancer

  • tumours blocking the digestive system

  • too much calcium in the blood

  • having a slow gut

  • emotional effects

  • raised pressure from a brain tumour

  • having advanced cancer

Chemicals made by the 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.

Tumours blocking the digestive system

Cancer that grows in the digestive system (for example, in your bowel or stomach) can stop food from passing through. Cancer can also grow around the digestive system causing a blockage. These are common causes of feeling sick.

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 medicines 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.

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

  • drowsy

You might also pass a lot of urine as your body tries to get rid of the extra calcium. You might feel confused or like your thinking is muddled.

Hypercalcaemia can be dangerous if is not treated, it can make you drowsy and difficult to wake. If it is left untreated, you could eventually become unconscious.

You might have regular blood tests to check your blood calcium levels. 

Contact your treatment team if you have any symptoms of high calcium. Your specialist will treat you if you have high calcium levels. You might have to have treatment in hospital but there are ways to manage it.

Slow gut

The digestive system can sometimes slow down due to:

  • cancer in the abdomen pressing on the muscles or lining of the bowel
  • cancer pressing on the nerves that supply the bowel (called the coeliac plexus)

As food does not pass through the bowel as quickly as normal this can make you feel sick. This is sometimes called a slow or sluggish gut.

Emotional effects

Emotional pain, being very nervous or worried about cancer and its treatment can make you feel sick or even be sick. For some people even seeing chemotherapy can make them feel sick or be sick due to previous experience.

Sometimes talking about your situation can help to reduce your worry and so reduce sickness.

Raised pressure from a brain tumour

A brain tumour or a cancer that has spread to your brain (secondary brain tumour) can 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. This is called raised intracranial pressure (raised ICP).

The increase in pressure causes:

  • sickness
  • headache
  • drowsiness

Sickness in advanced cancer

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 may 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

There are different ways of controlling sickness in advanced cancer to make you feel more comfortable.

  • DeVita, Hellman, and Rosenberg's Cancer: Principles & Practice of Oncology (12th edition)

    VT DeVita, SA Rosenberg and TS Lawrence

    Wolters Kluwer, 2023

  • Palliative Care and the Management of Common Distressing Symptoms in Advanced Cancer: Pain, Breathlessness, Nausea and Vomiting, and Fatigue

    LA Henson and others

    Journal of Clinical Oncology, 2020. Volume 38, Issue 9

Last reviewed: 
09 Aug 2023
Next review due: 
09 Aug 2026

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