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How chemotherapy kills cancer cells

Chemotherapy kills cells that are in the process of splitting into 2 new cells. This is how normal body tissues grow. But cancer cells divide much more often than normal cells, so they are more likely to be killed by chemotherapy.

Chemotherapy kills dividing cells by damaging the part of the control centre inside each cell that makes it divide. Some drugs interrupt the chemical processes involved in cell division.

Chemotherapy causes side effects because it affects healthy body tissues where cells are constantly growing and dividing. These tissues include the skin, bone marrow, hair follicles and lining of the digestive system. Normal cells can replace or repair cells that are damaged by chemotherapy. So side effects caused by damage to healthy body tissues usually go away once the treatment ends.

How you have chemotherapy

The main ways you can have chemotherapy are as an injection, a drip into the bloodstream, or tablets or capsules. The chemotherapy drugs circulate all round the body in the bloodstream to reach the cancer cells. Doctors call this systemic treatment.

How well chemotherapy works

You may have chemotherapy to try to cure your cancer or you may have it to control the cancer. The chance of the chemotherapy curing your cancer depends on the type of cancer you have. You may have chemotherapy on its own or with other treatments, such as surgery or radiotherapy.

Even if a cancer can’t be cured, you may have chemotherapy to help control a cancer by shrinking it, or to relieve symptoms.

PDF Download symbol You can view and print the quick guides for all the pages in the About Chemotherapy section.

 

How chemotherapy kills cancer cells

Chemotherapy kills cells that are in the process of splitting into 2 new cells. This is how normal body tissues grow. But cancer cells divide much more often than normal cells. So they are more likely to be killed by chemotherapy.

Body tissues are made of billions of individual cells. Once we are fully grown, most of the body's cells don't divide and multiply much. They only divide if they need to repair damage. When cells divide they split into 2 identical new cells. So, where there was 1 cell, there are now 2 and these then divide to make 4 and then 8 and so on.

In cancer, the cells keep on dividing until there is a mass of cells. This mass of cells becomes a lump - a tumour. Because cancer cells divide much more often than most normal cells, they are more likely to be killed by chemotherapy.

Some chemotherapy drugs kill dividing cells by damaging the part of the cell's control centre that makes it divide. Other drugs interrupt chemical processes involved in cell division.

The main ways you can have chemotherapy are as

  • An injection into the bloodstream (usually through a vein)
  • A drip (intravenous infusion) into the bloodstream through a vein
  • Tablets
  • Capsules

Chemotherapy drugs that you have in these ways circulate all round the body in the bloodstream. They can reach cancer cells almost anywhere in the body. This is known as systemic treatment.

You can find out about other less common ways of having chemotherapy in this section.

There is information about how normal cells grow and about how cancer cells differ from normal cells in the cancers in general section.

 

How chemotherapy kills dividing cells

Chemotherapy damages cells as they divide. In the centre of each living cell is a dark blob, called the nucleus. The nucleus is the control centre of the cell. It contains chromosomes, which are made up of genes. These genes have to be copied exactly each time a cell divides into 2 to make new cells.

Chemotherapy damages the genes inside the nucleus of cells. Some drugs damage cells at the point of splitting. Some damage the cells while they are making copies of all their genes before they split. Cells that are at rest, for instance most normal cells, are much less likely to be damaged by chemotherapy. You may have a combination of different chemotherapy drugs. The combination will include chemotherapy drugs that damage cells at different stages in the process of cell division. So, with more than one type of drug, there is more chance of killing more cells.

The fact that chemotherapy drugs kill dividing cells helps to explain why chemotherapy causes side effects. It affects healthy body tissues where the cells are constantly growing and dividing. The skin, bone marrow, hair follicles and lining of the digestive system are examples of cells that are constantly growing and dividing. 

  • Your hair is always growing
  • Your bone marrow is constantly producing blood cells
  • The cells of your skin and the lining of your digestive system are constantly renewing themselves.

Because these tissues have dividing cells they can be damaged by chemotherapy. But normal cells can replace or repair the healthy cells that are damaged by chemotherapy. So the damage to healthy cells doesn't usually last. Most side effects disappear once your treatment is over, and some only happen during the days while you are actually having the drugs, for example, sickness or diarrhoea. The section about cancer drug side effects explains this in detail.

 

How well chemotherapy works

The chance of the chemotherapy curing your cancer depends on the type of cancer you have

  • With some types of cancer most people are cured by chemotherapy
  • With other types of cancer fewer people are completely cured

Examples of cancers where chemotherapy works very well are testicular cancer and Hodgkin lymphoma.

With some cancers, chemotherapy can't cure the cancer on its own. But it can help in combination with other types of treatment. For example, many people with breast or bowel cancer have chemotherapy after surgery to help lower the risk of the cancer coming back.

With some cancers, if a cure is unlikely, your doctor may still suggest chemotherapy to

  • Shrink the cancer
  • Relieve your symptoms
  • Give you a longer life by controlling the cancer or putting it into remission
 

What remission means

Remission is a word doctors often use when talking about cancer or leukaemia. It means that after treatment there is no sign of the cancer. You may hear your doctor talk about complete remission and partial remission.

Complete remission means that the cancer or leukaemia can't be detected on scans, X-rays, or blood tests, etc. Doctors sometimes call this a complete response. 

Partial remission means the treatment has killed some of the cells, but not all. The cancer has shrunk, but can still be seen on scans and doesn't appear to be growing. The treatment may have stopped the cancer from growing. Or the treatment may have made the cancer smaller so that other treatments are more likely to help, such as surgery or radiotherapy. This is sometimes called a partial response. 

Another term doctors use is stable disease. This can mean that the cancer has stayed the same size or it may even have grown by a small amount.

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Updated: 7 March 2013