Why do cancers come back?

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

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

When doctors first diagnose cancer, they often give treatment 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. This is 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 may also be used. These include:

Using other treatments is called adjuvant treatment. Some people have treatment before an operation. This is called neo-adjuvant treatment.

For some types of cancer, such as leukaemia and lymphoma, an operation is not 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. You may have a combination of treatments, 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. This can sometimes happen many years later.

If cancer comes back in the same area of the body, it is called a local recurrence. If cancer develops in a different part of the body, it is 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. This includes a video of Amanda talking about her experience of advanced cancer.

Back to Understanding secondary breast cancer