Why do cancers come back?

When you are first diagnosed with cancer, treatment is usually given to try to get rid of the cancer. Your doctor will decide which type of treatment you need. They will use a treatment or combination of treatments to help reduce the chances of any cancer cells remaining.

Unfortunately, cancer cells are sometimes left behind after treatment. If this happens, the cancer may come back. This can happen years after your initial treatment. Cancer can come back in the same area of the body or somewhere else in the body. Cancer that returns:

  • in the same area of the body is known as a local recurrence
  • in a different part of the body is called a metastasis or secondary cancer.

Usually, treatment is used to control the cancer when it comes back. It is sometimes possible to use treatment to try and get rid of the cancer.

Why do cancers come back?

Sometimes cancer can come back. This can happen because tiny cancer cells, which can’t be seen with the naked eye or on scans, can sometimes be left behind after cancer treatment.

Over time these cancer cells can begin to divide again and form a tumour.

Treatment is often given to try to get rid of all the cancer so that it doesn’t come back. Many people have an operation to remove a tumour. Some healthy tissue around the tumour will also be removed to try to make sure all the cancer cells are taken away during the operation. To help reduce the risk of any cancer cells being left behind after surgery, other treatments such as chemotherapy, radiotherapy and targeted (biological) therapy may also be used. This is known as adjuvant treatment. Treatment can also be given before an operation – this is called neo-adjuvant treatment.

For some types of cancer, such as leukaemia and lymphoma, an operation isn’t appropriate. In this case chemotherapy, radiotherapy or targeted therapy may be used. These treatments aim to destroy as many of the cancer cells as possible. Often a combination of treatments is given, which can be more effective.

Unfortunately, no treatment is guaranteed to be 100% effective. Sometimes cancer cells can remain and in some people the cancer might come back - sometimes many years later.

If cancer comes back in the same area of the body it’s known as a local recurrence. If cancer develops in a different part of the body, it’s called a secondary cancer or metastasis. A secondary cancer can develop if cancer cells break away from the original (primary) cancer and spread to other organs in the body through the bloodstream or lymphatic system. When these cells reach a new area of the body they grow to form a new tumour. Recurrent and secondary cancers are sometimes called advanced cancer.

If cancer does come back it can often be treated again. Usually in this situation, treatment is given to control the cancer, sometimes for many months or years. In some situations it may be possible to give treatment that aims to get rid of the cancer again.

We have more information about advanced cancer, including a video of Amanda explaining her experience of advanced cancer.

Back to Understanding

What is cancer?

There are more than 200 different kinds of cancer, each with its own name and treatment.

Cancer and cell types

Cancers are grouped into types. Types of cancer often behave and respond to treatments in different ways.

How is it treated?

There are five main types of cancer treatment. You may receive one, or a combination of treatments, depending on your cancer type.