What is cancer of unknown primary (CUP)?

Primary cancer means where the cancer started. 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.

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 tumour.

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 can spread to more than one part of the body. People with CUP sometimes have more than one secondary cancer.

Why can the primary cancer not be found?

A primary cancer cannot always be found. This may be because:

  • it is too small to be seen on scans
  • it is hidden beside or behind a larger secondary cancer
  • the body’s immune system has got rid of it, but the secondary cancer is still growing.

Symptoms

Symptoms of CUP depend on where the secondary cancer is in the body. We have more information about symptoms of cancer that has spread to the:

General symptoms of cancer include:

  • unexplained weight loss
  • loss of appetite
  • feeling extremely tired all the time
  • looking pale, and feeling tired and breathless – this may be caused by a low level of red blood cells (anaemia).

All the symptoms mentioned here can be caused by conditions other than cancer. But it is important to see your GP and get them checked.

Diagnosis

If you have symptoms, you usually start by seeing your GP. 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.

The specialist will arrange any tests you need and may also consider any risk factors you have, such as:

  • whether you have a strong family history of cancer 
  • whether you have a condition that increases your risk of cancer
  • your lifestyle, for example if you smoke or drink large amounts of alcohol
  • if you have been exposed to asbestos or chemicals that increase the risk of certain cancers, for example in your job.

Doctors may look for the most common types of primary cancers first. This include breast or prostate cancer. The tests might show you have cancer, but the doctors still may not know where the cancer started. In this situation you will be referred to a specialist CUP team. The CUP specialist doctors may want to do more tests. They 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.

Waiting for test results can be a difficult time. We have more information that may help. If your cancer is confirmed as CUP, you will be introduced to a nurse who specialises in this type of cancer. You will get their contact details.

You may have some of the following tests:

  • Blood tests

    Blood tests ultrasound scan can help your doctors know which area of the body it might be helpful to scan.

  • X-rays and scans

    You may have x-rays or scans to check part of the body. We have more information about x-ray, mammograms, CT scan, PET-CT scans, MRI scan, ultrasound scan.

  • Cameras that look inside the body (endoscopy)

    An endoscopy is a test that looks inside the body using a thin, flexible tube with a camera on the end. This test may have different names depending on the area of the body. For example, a colonoscopy is a test to look inside the bowel. If you know the name of the test you are having, you can find it in our A-Z of tests.

  • Laparoscopy

    A laparoscopy is a small operation to look at organs inside your tummy (abdomen).

  • Biopsy

    If tests show that you might have cancer, you may have a biopsy. A biopsy means taking a sample of tissue or cells from an abnormal area. The sample is checked under a microscope for cancer cells. It may be tested to find out more about the type of cancer.

Having tests can take up a lot of energy and time. Some tests might give more information about the cancer. But they might not change what treatment you will be offered or your overall care. In this situation, you may choose not to have them.

Your cancer doctor might recommend that you:

  • start treatment, rather than have more tests
  • start treatment while you are still having tests.

They will explain which option they think will help most in your situation.

Treatment

When CUP is diagnosed, cancer has already spread from one part of the body to another. In many cases, this means the cancer is already advanced. It is not usually possible to cure cancer that is advanced and has spread to other parts of the body. The aim of treatment for CUP is to try to:

  • control the cancer
  • help you live longer
  • treat your symptoms.

A team of specialists will meet to discuss the best possible treatment for you. This is called a multidisciplinary team (MDT). Your cancer doctor or specialist nurse will explain the different treatments and their side effects. They will also talk to you about things to consider when making treatment decisions.

The following treatments may be used to treat CUP. We have more information about treating CUP that explains when each treatment may be used. You may have one treatment or a combination of treatments. You may be offered some as part of clinical trials.

  • Chemotherapy

    Chemotherapy uses anti-cancer (cytotoxic) drugs to destroy cancer cells. This is often the main treatment for CUP because chemotherapy goes into the bloodstream. This means it can reach most parts of the body.

  • Radiotherapy

    Radiotherapy uses high-energy rays to destroy cancer cells. You may have this treatment to treat an area of cancer in the body. It can be used to try to shrink and control the cancer, and stop it from growing any further. It may also be given to try and improve any symptoms (palliative radiotherapy).

  • Hormonal therapies

    Hormonal therapy drugs are used to treat types of cancer that are encouraged to go grow by hormones. They are most commonly used to treat breast cancer and prostate cancer.

  • Steroids

    Steroids are substances that are naturally produced in the body. But they can be made artificially as drugs. Steroids can be used to help improve some symptoms. They are sometimes also used as part of chemotherapy treatment.

  • Targeted therapies

    There are many different types of targeted therapy drugs. Each type targets something in or around the cancer cell that is helping it grow and survive.

  • Surgery

    Surgery is not often used to treat CUP. But in some situations, you may have an operation to remove a secondary cancer.

Treating symptoms

For many people with CUP, the main aim of their treatment is to control symptoms. Symptoms can be treated using cancer treatments, such as radiotherapy. But they can also be managed using supportive treatments, such as painkillers or steroids or with help from healthcare professionals, such as dietitians or physiotherapists.

Your cancer doctor may refer you to a palliative care team. This team specialises in managing pain and other symptoms. They are also experts in giving emotional support to patients and their families.

You can have supportive care alongside cancer treatments, and after they are finished. You may decide to have supportive care on its own, without cancer treatments.

There are different symptoms, and many of them depend on where the secondary cancer is. We have more information about managing:

If you need information about managing another symptom, you can search using our A-Z list or call us on 0808 808 0000.

After treatment

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.

Reviewed: 30 June 2019
Reviewed: 30/06/2019
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Next review: 31 December 2021
Next review: 31/12/2021