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  • What is cancer of unknown primary?

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    What is cancer of unknown primary (CUP)?

    This is a secondary cancer that has spread to a new location from somewhere else in the body. However, it’s not clear where in the body it started, so the primary cancer is unknown.

    For most people diagnosed with cancer, the primary cancer is easy to identify. Doctors conduct tests to find out where the cancer started to grow and to see if the cancer has spread.

    When cancer is found in one or more secondary sites but it is not clear from the test results where the cancer began, the cancer is usually known as cancer of unknown primary, or CUP. Health professionals may also call it tumour of unknown origin (TUO), metastatic malignancy of unknown primary, or occult primary cancer.

    Because it is a secondary cancer, CUP is considered advanced cancer. This means that in some cases, treatment focuses on controlling symptoms. In other cases, doctors actively treat the cancer while still making sure that symptoms are well managed. Your doctor will discuss the best approach for you.

    How can doctors tell it is a secondary cancer?

    To diagnose secondary cancer, a specialist doctor called a pathologist examines the cancer cells under a microscope. The pathologist can see that the cancer cells do not belong to or originate in the surrounding tissue, and this can be confirmed by further laboratory tests. With CUP, the cells could possibly have come from a number of places but no primary cancer can be found.

    Why can't the primary cancer be found?

    There could be several reasons why the primary cancer cannot be found. It may be that:

    • the secondary cancers have grown and spread quickly, but the primary cancer is still too small to be seen on scans
    • your immune system has destroyed the primary cancer, but not the secondary cancer
    • the primary cancer cannot be seen on x-rays, scans or endoscopies because it is hidden by a secondary cancer that has grown close to it
    • the primary cancer has been removed during surgery for another condition without doctors realising the cancer was there, so some cancer cells remained behind and have since spread
    • there may never have been a primary cancer massa single cell may have changed into cancerous cells and then spread through the body. 

    Will I need lots of tests?

    Many people find they need several tests to try to find where the cancer started. The tests may take time and be tiring, particularly if you are feeling unwell. You may also feel frustrated if the tests don’t find the primary cancer.

    Your doctors will only suggest tests they feel are necessary. It is okay to ask them to explain the tests and what difference the results will make to your care. With this information, you can weigh up the potential benefits of the tests and make an informed decision about having them. At some point, your doctors may decide that having more tests won’t help find the primary site. It may be of more benefit to focus on your treatment even if the primary cancer can’t be found.

    If you do decide against having further tests, you may find your family and friends encourage you to continue. This can be a challenging situation, and it may help to explain your reasoning to them.

    What are the symptoms?

    Symptoms are different for everyone and are related to the area where the secondary cancer is found. Some people with CUP have few or no symptoms; others have a range of symptoms that may include:

    • shortness of breath
    • cough
    • bone pain and/or back pain
    • swelling and discomfort in the abdomen, feeling sick (nausea), fluid collecting in the abdomen (ascites)
    • yellowing of the skin and eyes (jaundice)
    • swollen lymph nodes in the neck, underarm, chest or groin
    • looking pale, feeling tired and becoming breathless due to a lack of red blood cells (anaemia).

    You may also have general symptoms such as unexplained weight loss, poor appetite, night sweats or fatigue. Not everyone with the symptoms listed above will have CUP, but see your general practitioner (GP) if you are concerned.

    How common is CUP?

    CUP is diagnosed more often than many people realiseit is the 11th most common cancer in Australian women and the 12th most common cancer in Australian men.

    There are nearly 3,000 new cases of CUP diagnosed each year in Australia. For both men and women, CUP is more likely to occur over the age of 60.

    What are the different types of CUP?

    Even if tests can’t find where the cancer started, your doctor will try to work out what type of cell the cancer developed from. Knowing the type of cell helps doctors work out what sort of treatment is most likely to be helpful.

    In about 95 per cent of people with CUP, doctors can tell that they have some sort of carcinoma. Carcinoma means any cancer that begins in the cells lining the skin and internal organs (epithelial cells). There are different types of carcinoma depending on which type of epithelial cells are affected.

    There are other forms of cancer that are not carcinomas. For example, lymphomas begin in the cells of the immune system, melanomas begin in the cells that give skin its pigment, and sarcomas begin in the cells of muscles, fat and other connective tissue.

    This website page was last reviewed and updated February 2018.

    Information reviewed by: A/Prof Linda Mileshkin, Medical Oncologist, Peter MacCallum Cancer Centre, VIC; Dr Sarwan Bishnoi, Medical Oncologist, Adelaide Cancer Centre, SA; Dave Clark, Consumer; Dr Jan Maree Davis, Area Director, Palliative Care Service, Calvary Health Care and St George Hospital, NSW; Linda Tompsitt, Cancer Nurse 13 11 20, Cancer Council WA; Catherine Trevaskis, Gastrointestinal Cancer Specialist Nurse, The Canberra Hospital, ACT.

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