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Cancers sometimes come back

Nurse and patients talking about cancer   

This page tells you about how cancer can sometimes come back after it has been treated. There is information on


Why cancer might come back

Cancer may come back some time after its initial treatment. This idea can be frightening. There are a number of different explanations for why cancer might come back. But the main reasons are that some cancer cells have

  • Been left in the body where the original cancer was
  • Spread to other parts of the body and gradually grown to form a new tumour

It may help to look at our section on cells and cancer to understand how cancers develop and how cancers spread.

Cancer may come back after any type of treatment.


After surgery

Cancer can come back after surgery because

  • There were cancer cells left behind during the operation
  • Some cancer cells had broken away from the primary cancer before the operation and spread to elsewhere in the body

Surgeons do their best to make sure that all the primary cancer is removed. But no medical scan has been invented that can pick up one cell, or small groups of cells that have spread. Your surgeon can give you an educated guess about whether your cancer is likely to have been cured by your surgery. And adjuvant treatment can be given to try to kill any cells that have escaped.


After chemotherapy and radiotherapy

Cancer cells are killed by chemotherapy drugs because these drugs attack cells that are in the process of doubling to form two new cells. Cells that are actively dividing are also more vulnerable to radiation, although it is not fully understood why this is. So radiotherapy works by killing dividing cells too.

But not all the cells in a cancer will be dividing at the same time. Normal cells go into a long rest period between divisions. Cancer cells do too, although the rest period may be much shorter.

Giving chemotherapy and radiotherapy in a series of treatments helps to catch as many cells dividing as possible and so kill them. Hopefully, cells that were resting when you had your first treatment (so didn't die) will be active when you have your next and so will be more likely to die.

But it is unlikely that any cancer treatment will kill every single cancer cell in the body. To do that, the treatment would have to be very strong and would have too many dangerous side effects. What doctors are trying to do is to reduce the numbers of cancer cells so much that there are too few cells left for the cancer to survive. They hope the remaining cells will be killed off by the body's own defences or will just die off naturally, as many cancer cells do when they leave the primary tumour.

Your doctors will want to give you as much treatment as they can. But they can't give you more than is safe. All treatments have a safe limit. You can only have up to a certain amount of radiotherapy to any particular part of the body. If you have more, then normal body tissue will be too damaged to repair itself.

Chemotherapy and biological therapy drugs have their limits too. Some can cause problems with the heart, liver, lungs or kidneys, so the dosage has to be carefully calculated.


Cure or remission

These days many cancers are cured. But some cancers can come back many years after they have first been treated. So you may find your doctor very unwilling to use the word 'cure' even though there is no sign that you have any cancer left. Your cancer will be said to be in remission. This means there is no sign of cancer in your body. If there are any cancer cells left

You may be on some type of long term treatment to try to keep any remaining cancer cells in an inactive state – for example, hormonal therapy for breast cancer. Being on this type of long term treatment doesn't mean your cancer is definitely still there. You may have been cured, but the doctor cannot know this.


Living with uncertainty

It can be extremely difficult to live with the fact that your cancer may come back. Even if your doctors tell you they are 95% certain your cancer has gone for good, you may find it very upsetting that no one can say "Yes, you are cured". 

Some people find they cannot stop thinking about having had cancer, even though they expected to put it behind them once their treatment had finished. You may feel a little frightened of planning anything in the future or you may feel sad or depressed.

For most people who are in this situation, each day lowers the risk of a recurrence. Most cancers that are going to come back will do so in the first two years after treatment. After five years you are even less likely to get a recurrence. For some cancers, after 10 years your doctor may say you are cured.

Unfortunately, some types of cancer can come back many years after they were first diagnosed. If you are finding it hard to get over having had cancer you may find it helpful to talk to other people in the same situation or to a trained counsellor. This can help you to find ways of dealing with the fear and worry. Try contacting one of the organisations that offer information or counselling. 

You can look at our section about coping with cancer

You might also like to look at our online forum, Cancer Chat.

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Updated: 24 July 2013