Cancer of unknown primary (CUP)

Primary cancer means where the cancer started. The part of the body where the cancer first started to grow is called the primary site. The cancer type is usually named after the part of the body where it first started to grow. For example, a cancer that starts in the lung is called a primary lung cancer.

A secondary cancer happens when cancer cells separate from a primary site and spread to another part of the body. The cancer cells travel through the blood or lymphatic system and form a new cancer somewhere else in the body.

A secondary cancer is also called a metastasis or metastatic cancer. It is made up of the same type of cancer cells that formed the primary cancer. For example, a cancer that starts in the lungs and spreads to the liver is made up of lung cancer cells, not liver cancer cells.

Cancer of unknown primary (CUP) means that your doctor is not sure where the cancer started. They have found a secondary cancer but have not been able to find the primary cancer. People with CUP sometimes have secondary cancer in more than 1 part of the body

With CUP, doctors cannot always tell which part of the body the cancer cells are from. But cancers are made up of different types of cells. These can be grouped based on the type of cells they are made up of. Knowing the type of cell can give the doctors a better idea about where the cancer may have started. This helps them to plan the best treatment.

We have more information about CUP and different cell types.

Sometimes doctors cannot find out where the primary cancer started. This may be because:

• the primary cancer is too small to be seen on scans
• the primary cancer is hidden by a larger secondary cancer
• the body’s immune system has destroyed it, but it has already spread.

Doctors might stop looking for the primary cancer if:

• you are not feeling well enough to have tests
• further test results are unlikely to change your treatment plan.

If you have symptoms, you usually start by seeing your GP. They will examine you and ask about your symptoms. If they think you might have cancer, they may refer you to a specialist for tests. Or if you have symptoms that are making you very unwell, you may be admitted to hospital straight away. In this situation, you will have tests while you are staying in hospital as an inpatient.

The first specialist doctor you see and the tests you have depend on your symptoms. For example,

• if you have bowel or stomach symptoms, your GP will refer you to a gastroenterologist. They treat problems of the digestive system.
• if you have kidney or bladder symptoms, you will see a urologist. They treat problems of the urinary system.

Doctors may look for the most common types of primary cancers first. The tests might show you have cancer, but the doctors still may not know where the cancer started. In this situation, the GP may refer you directly to a particular hospital team. This could be:

• the malignancy of unknown origin (MUO) team
• the cancer of unknown primary (CUP) team
• a rapid diagnostic centre.

The specialist team will arrange any tests you need. The tests you have depend on your symptoms. Your doctor will use national guidelines to decide which tests are right for you. The results of one test may suggest that another one would be useful.

You might have some of the following tests and scans:

Other tests on the biopsy

Some other tests can be done on a biopsy sample. They may give doctors more information about the type of cancer you have.

You might have some of the following tests and scans:

Waiting for test results

Waiting for test results can be a difficult time. It may take from a few days to a couple of weeks for the results to be ready. You may find it helpful to talk with a partner, family member or close friend. Your specialist nurse or a support organisation can also provide support. Or you can talk to one of our cancer support specialists for free on 0808 808 00 00 (7 days a week, 8am to 8pm).

Being diagnosed with cancer of unknown primary can make you feel shocked, frightened, angry or upset. There is no right or wrong way to feel. It may help to get support from family, friends or a support organisation.

Macmillan is also here to support you. If you would like to talk, you can:

• call the Macmillan Support Line on 0808 808 00 00
• chat to us online
• visit our cancer of unknown primary forum to talk with people who have been affected by cancer of unknown primary, share your experience, and ask an expert your questions.

When your treatment has finished, you will have regular check-ups. You may also have follow-up scans. How often you have them will depend on your treatment plan:

• If the aim of treatment was to cure the cancer, you may see your cancer doctor or specialist nurse every few months for up to two years.
• If the aim of treatment was to control the cancer, you may see your cancer doctor or specialist nurse less often.

Your cancer doctor and specialist nurse will give you advice on what to look out for. If you have any problems or notice new symptoms between check-ups, tell them as soon as possible.