How chemotherapy works

Chemotherapy works by killing cancer cells. It has different effects on different types of cancer. 

How cancer develops

Body tissues are made of billions of individual cells. When cells divide, they split into 2 identical new cells. So where there was 1 cell, there are now 2. Then these divide to make 4, then 8 and so on.

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.

In the centre of each living cell is its control centre. This is called the nucleus. It contains chromosomes, which are made up of genes.

These genes are copied exactly each time a cell divides into 2 new cells.

Diagram showing how new genes are made for new cells

In cancer, the cells keep on dividing until there is a mass of cells. This mass of cells becomes a lump, called a tumour.

How chemotherapy effects dividing cells

Chemotherapy kills cells that are in the process of dividing into 2 new cells. It damages the genes inside the nucleus.

Different chemotherapy drugs will do this in different ways. They might:

  • damage the part of the cell's control centre that make it divide

  • interrupt the chemical processes involved in cell division

  • damage the cells while they're making copies of all their genes before they divide

  • damage cells at the point of division

Cancer cells divide much more often than most normal cells. So chemotherapy is much more likely to kill them. Chemotherapy is less likely to damage cells that are at rest, such as most normal cells. 

You might have a combination of different chemotherapy drugs. This includes drugs that damage cells at different stages of cell division. This means there's more chance of killing more cells.

Why chemotherapy causes side effects

Chemotherapy doesn’t only kill cancer cells. It also affects healthy body tissues where the cells are constantly growing and dividing, such as:

  • your hair

  • your bone marrow

  • your skin and the lining of your digestive system

The damage to these cells can cause side effects. 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. Some side effects such as sickness or diarrhoea might only happen during the days you are having the drugs. 

How you have chemotherapy

You usually have chemotherapy as one or more of the following:

  • an injection into the bloodstream (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 around the body in the bloodstream. They can reach cancer cells almost anywhere in the body. This is known as systemic treatment.

How well chemotherapy works

The chance of the chemotherapy curing your cancer depends on the type of cancer you have. 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. This helps to lower the risk of the cancer coming back.

Even if your cancer can’t be cured, your doctor may still suggest chemotherapy to:

  • shrink the cancer

  • relieve your symptoms

  • give you a longer life by controlling the cancer

What remission means

These days, doctors are able to cure many cancers. But some cancers can come back many years after treatment. So you may find that your doctor is very unwilling to use the word 'cure'. Remission is a word doctors often use when talking about cancer. It means that after treatment there is no sign of the cancer.

You might hear your doctor talk about complete remission, partial remission or stable disease.

Complete remission

This means that the cancer can't be detected on scans, x-rays, blood tests or other tests. Doctors sometimes call this a complete response. Or they might say there is no evidence of disease. 

Partial remission

This means the chemotherapy has killed some of the cells, but not all.

The treatment might have shrunk the cancer and stopped it from growing. Or it could have made it smaller so that other treatments are more likely to help, such as surgery or radiotherapy.

This is sometimes called a partial response. 

Stable disease

This means that the cancer has stayed the same size or it might even have grown by a small amount.

  • Clinical Oncology (5th edition)
    P Hoskin
    Taylor and Francis, 2020

  • Cancer Chemotherapy: Basic Science to Clinic
    GS Goldberg and R Airley
    John Wiley and sons, 2020

  • The Royal Marsden Manual of Clinical and Cancer Nursing Procedures (10th edition, online)
    S Lister, J Hofland and H Grafton 
    Wiley Blackwell, 2020

  • Cancer and its Management (7th edition)
    J Tobias and D Hochhauser
    Wiley Blackwell, 2015

  • Handbook of Cancer Chemotherapy (8th edition)
    RT Skeel and SN Khleif
    Lippincott, Williams and Wilkins, 2011

Last reviewed: 
16 May 2024
Next review due: 
17 May 2027

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