How chemotherapy works
This page explains how chemotherapy works. There is information about
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 spend most of their time in a resting state and only divide if they need to repair damage. When cells divide they split into two, 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. The lump is called a tumour. Cancer cells divide much more often than most normal cells.
Chemotherapy enters the bloodstream and damages dividing cells. Cells in the process of dividing are more at risk of being damaged by chemotherapy. Chemotherapy kills the cell by damaging the part of the control centre inside each cell that makes cells divide. Or it may interrupt the 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
The chemotherapy drugs circulate all round the body in the bloodstream and 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.
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.
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's 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
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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