What is cancer of unknown primary?

Cancer of unknown primary (CUP) is when cancer cells are found in the body but the place the cancer began is not known. This means it is a secondary cancer that has spread to a new place from an unknown primary cancer somewhere else in the body.

With CUP, secondary cancers are commonly found in the liver, lung, abdomen, bones and lymph nodes, although they can grow in any part of the body.

Health professionals may also call CUP metastatic malignancy of unknown primary or occult primary cancer.

How do doctors know that it is a secondary cancer?

To diagnose secondary cancer, a specialist doctor called a pathologist looks at the cancer cells under a microscope. They can see that the cancer cells do not belong to the surrounding tissue, and this can be confirmed by further tests on the cells. With CUP, there are many different places in the body the cancer cells might have started.

Why can’t the primary cancer be found?

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 it has spread. Sometimes, however, cancer is found in one or more secondary sites and test results can’t show where the cancer began.

Reasons why your doctors cannot find the primary cancer include:

• the secondary cancer has grown quickly, but the primary cancer is still too small to be seen on scans or found on tests
• your immune system has destroyed the primary cancer, but not the secondary cancer
• the primary cancer can’t be seen on x-rays, imaging scans or endoscopies because it’s hidden by a secondary cancer that has grown close to or over it
• the cancer may be found in many parts of the body, but it isn’t clear from the scans or pathology tests which is the primary cancer.

Does it matter that the primary cancer can't be found?

Finding the primary cancer can help doctors decide what treatment to recommend and give them a better idea of how the cancer is likely to respond to treatment. If the primary cancer can’t be found, tests on cells from the secondary cancer can often suggest what the primary cancer is most likely to be. This helps your doctor to plan treatment.

Can CUP be treated?

It can be frightening to be diagnosed with CUP, but there are treatments available. Your doctor will discuss the best options for you. The aim of treatment may be to:

• Slow the cancer’s growth or spread and prolong overall survival – In many cases, doctors may actively treat the cancer but not be able to cure it. In some cases, CUP presents in a pattern that is very like cancers from a known primary and can respond well to the same kind of treatment, even though the primary can’t be found.
• Relieve symptoms and maintain quality of life – CUP usually presents as advanced cancer, so treatment may focus on controlling symptoms and helping you plan the best possible future care for yourself. This is known as palliative treatment.
• Remove as much of the cancer as possible – In a small number of cases, CUP is found as a small area of cancer that may be able to be removed with surgery or high-dose radiation.

“I have found it complex to talk to people about my cancer. …It seems incomprehensible to have a cancer that has spread but has no named starting point.” Jane

Will I need lots of tests?

Most people with a new diagnosis of cancer need several tests to find out how far the cancer has spread throughout the body.

People with CUP may need extra tests to try to find where the cancer started. The tests may take time and be tiring, particularly if you are feeling unwell. Waiting for the results can be a stressful time. You may also feel frustrated if the tests don’t find the primary cancer.

Your doctors will only suggest tests that they think are needed. It is okay to ask your doctors to explain the tests and the difference the results will make to your care. You may also want to ask if there are any specialised tests available at another hospital or treatment centre that may help find the primary cancer.

At some point, your doctors may decide that more tests won’t help find the primary cancer and it would be better to focus on starting treatment. Even if you decide not to have more tests, your family and friends may want you to have more tests. It may help to explain why you want to stop testing and share this booklet with them. Your medical team can provide support with these discussions.

What are the symptoms?

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

• swollen lymph nodes in the neck, underarm, chest or groin
• a lump or thickening
• feeling very tired (fatigue)
• poor appetite and/or feeling sick (nausea)
• unexplained weight loss
• fevers and night sweats
• cough, shortness of breath or discomfort in the chest
• pain in the bones, back, head, abdomen or elsewhere
• swelling of the abdomen
• change in bladder habits, such as needing to pee more often
• change in bowel habits, such as constipation or diarrhoea
• yellowing of the skin and eyes (jaundice).

Not everyone with the symptoms listed above will have cancer, but see your general practitioner (GP) if you are concerned.

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.

Most cancers are cancers of the epithelial cells, which are found in the lining of the skin and internal organs. These cancers are known as carcinomas. In most people with CUP, doctors can tell that they have some sort of carcinoma.

There are different types of carcinoma depending on which type of epithelial cell is affected (see below for more information). Your doctor will explain the type of CUP you have.

Types of CUP

Adenocarcinoma

Squamous cell carcinoma (SCC)

Neuroendocrine carcinoma

Poorly differentiated carcinoma

Undifferentiated neoplasm (tumour)

Which health professionals will I see? 

Your GP will arrange the first tests to assess your symptoms. If these tests do not rule out cancer, you will usually be referred to a specialist for further tests. The type of specialist you see will depend on your symptoms, the suspected location of the cancer and the types of tests you need.

For example, you may see a gastroenterologist (digestive tract, bowel or stomach), gynaecologist (female reproductive system), urologist (urinary tract or kidneys; male reproductive system), respiratory physician or thoracic surgeon (chest and lung), neurosurgeon (brain and spinal cord), ear nose and throat surgeon, or haematologist (blood cells).

Sometimes your main specialist will be a medical oncologist who treats all types of cancer. If cancer is diagnosed, the specialist will consider treatment options. Often these will be discussed with other health professionals at what is known as a multidisciplinary team (MDT) meeting.

During and after treatment, you will see a range of health professionals who specialise in different aspects of your care.

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