How chemotherapy drugs work
Chemotherapy drugs work by stopping cancer cells reproducing.
The drugs are carried in the blood so they can reach cancer cells anywhere in the body. Different drugs damage cancer cells in different ways. When a combination of drugs is used each drug is chosen for its different effects.
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Chemotherapy drugs are also taken up by some healthy cells. These healthy cells
can usually repair damage caused by chemotherapy but cancer cells can’t and eventually die.
The effect that chemotherapy drugs have on some of the healthy cells in your body can cause side effects. Most side effects will go away when treatment is over.
Healthy cells in certain parts of the body, such as the bone marrow (which makes blood cells) and the digestive system, are especially sensitive to chemotherapy drugs. This is why certain side effects, such as risk of infection or feeling sick, are more common. There’s information on side effects and how they can be reduced and managed in our section on side effects.
Monitoring the effects on the cancer
During treatment, your cancer doctor may want to find out how the cancer is responding to the chemotherapy drugs. This can be done in different ways.
If a cancer can be felt or is visible, your doctor will be able to tell if it’s responding to chemotherapy by doing a physical examination.
If the cancer can be seen on a scan, you may have another scan after a few treatments of chemotherapy to see if the cancer is getting smaller. If you’re having chemotherapy to reduce the risk of cancer coming back after surgery (adjuvant chemotherapy), you won’t usually need scans to check if it’s working.
With some cancers, blood tests can be used to check if treatment is working. These cancers release proteins in the blood (called tumour markers) that can be measured with a blood test. If the tumour markers are reducing it usually means the chemotherapy is working.
If results show the cancer hasn’t responded well enough, your doctor may decide to give you different chemotherapy drugs.