Why some cancers come back

This page tells you about how cancer can sometimes come back after treatment. There is information about

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 reasons for why cancer might come back. 

One reason is that the original treatment did not get rid of all the cancer cells and those that were left grew into a new tumour. Another is that some cancer cells have spread to other parts of the body and gradually grown there to form a tumour.

After surgery

Cancer can come back after surgery because

  • Some cancer cells were 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 it is always possible that a tiny group of cancer cells has been left behind. Your surgeon may recommend additional treatment if they feel that there is a risk that the cancer could come back. The extra treatment might be chemotherapy, radiotherapy, hormone therapy or biological therapy. These treatments aim to try to control or kill any cells that are left.

After cancer drug treatment or radiotherapy

Cancer may sometimes come back after cancer drug treatment or radiotherapy because the treatment did not destroy all of the cancer cells. 

Chemotherapy drugs kill cancer cells by attacking cells that are in the process of doubling to form two new cells. 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 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. Doctors try to reduce the numbers of cancer cells so much that the remaining cells will be killed off by the body's own defences. Or the cells may just die off naturally.

Radiotherapy makes small breaks in the DNA inside cells. These breaks stop cancer cells from growing and dividing, and often make them die. Normal cells close to the cancer can also be damaged by radiation but most of them recover and go back to working normally. If radiotherapy doesn't kill all of the cancer cells they will regrow at some point in the future.

Biological therapies control cancer by changing the growth processes in cancer cells. Some treatments may get rid of a cancer completely but others may shrink the cancer or control it for some months or years. So a cancer may seem to have gone and may not show up on any scans or blood tests. But there may be a small group of cells that remain in the body and start to grow and develop into a larger tumour after a while or when the treatment stops.

Cancers can become resistant to treatment

Sometimes cancer can become resistant to cancer drug treatment. Cancers develop from normal cells that have changed or mutated to become cancerous. The mutation Open a glossary item happens in the genes of the cell. These gene changes make the cell behave differently to a normal cell. Cancer cells continue to mutate, so that they become more and more abnormal. Sometimes the mutations make the cells resistant to cancer drugs such as chemotherapy, biological therapies or hormone therapy.

If this happens you can sometimes have a different type of treatment. But unfortunately, sometimes cancers develop resistance to many drugs at the same time. Doctors call this multi drug resistance. 

Scientists have found a group of genetic mutations that they think cause chemotherapy resistance. These mutations mean that the cancer cell can keep the drugs out. The resistant cells have high levels of a substance called p-glycoprotein. P-glycoprotein is a protein found in cell walls. The protein acts as a pump and removes toxins from cells. Cells with high p-glycoprotein levels are very good at keeping cancer drugs out. If there is not enough of the drug inside a cancer cell, the drug cannot kill the cell.

Researchers have been working on this problem almost as long as cancer drugs have been used. If we are to make cancer drug treatment more effective for more types of cancer we need to find a way of overcoming resistance.

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

  • There are too few to find
  • There are too few to cause any symptoms
  • They are in an inactive state and are not growing

Doctors can't be sure that the cancer has completely gone after treatment. So they may prescribe some type of long term treatment, such as biological therapy or hormone therapy. These treatments are called adjuvant treatment and aim to try to prevent the cancer coming back.

Living with uncertainty

It can be very 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 for sure "Yes, you are cured".

Some people find that they can't stop thinking about having had cancer, even though they expected to put it behind them after the end of their treatment. 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 or so after treatment. After five years you are even less likely to get a recurrence. For some types of cancer, after 10 years your doctor may say that you are cured.

Unfortunately, some types of cancer can come back many years after they were first diagnosed. Some people find it very difficult to cope with this idea.

Getting help and support

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 you could talk to a trained counsellor. This can help you to find ways of dealing with the fear and worry. 

You can get in touch with a counsellor by contacting one of the counselling organisations.

You can also look at our section about coping emotionally with cancer.

You can share your experiences with other people and find out how they coped by using our online forum, Cancer Chat.

Related information

You may find it helpful to read our information about how cancers grow.

We also have information about how cancer can spread.

You can read about cancer treatments.

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