Cancer of unknown primary

Monday 5 September, 2011

On this page: What is cancer of unknown primary? | Why can't the cancer be found? | Does it matter it can't be found? | Will I need lots of tests? | What are the different cell types? | What are the causes? | What are the symptoms? | How common is CUP? | Information reviewed by

What is cancer of unknown primary?

This is a cancer that has spread from somewhere else in the body, but it's not clear where in the body it started.

For most people who have cancer, the primary cancer is easy to identify. Doctors conduct tests to find where in the body the cancer started to grow. They may also do other tests to see if the cancer has spread.

When cancer is found in one or more secondary sites but the doctor can't tell from the test results where the cancer began, the cancer may be called cancer of unknown primary or CUP.

Why can't the primary cancer be found?

This may be for several reasons. Your immune system may have destroyed the primary tumour, but not the secondary tumours (metastases).

The secondary tumours may have grown and spread quickly, but the primary tumour is still too small to be seen on scans. The primary tumour may not be seen on x-rays or scans as it is hidden by secondaries that have grown close to it.

The primary cancer may have spread throughout the body then disappeared. It is thought that primary tumours of the lining of the digestive system (from the mouth to the anus) may occasionally be passed out of the body through the bowel.

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

Finding the primary cancer helps doctors decide what treatment to recommend. If it can't be found, the treatment path is less clear. However, doctors try to learn as much as they can about the spread of the cancer, the cells involved, your symptoms and medical history to help plan treatment.

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 site of the primary cancer.

You may want to talk to your doctor about how many tests you need. They will only suggest tests they feel are necessary. Ask your doctor or nurse to explain the tests you are having, as knowing more about the tests may help you make an informed decision.

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 you to focus on controlling the symptoms.

Even if you 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 decision to your loved ones.

What are the different cell types?

Even if tests can't find where the cancer started, your doctor will try to discover the type of cell the cancer developed from. Knowing the type of cell may give doctors a clue as to where the cancer started.

  • Adenocarcinoma - Most people with CUP have cancers that develop from glandular cells, which are found in many organs of the body. Common primary sites for adenocarcinomas include breast, colon, prostate, stomach, pancreas, liver and lung.
  • Poorly differentiated carcinoma - There is enough detail to tell that the cells are cancerous but they may look too abnormal to classify further under the microscope.
  • Squamous cell carcinoma - These cancers look like the flat cells that are normally found on the surface of the skin or the lining of certain organs. About 5% of people with CUP have squamous cell cancers. Common sites include the head and neck area, skin, oesophagus, lungs and cervix.

What are the causes?

Cancer is a group of more than 200 different diseases. Each type of cancer has different risk factors, such as getting older, poor diet, smoking, excessive alcohol consumption and being obese. These may play a role in CUP.

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
  • 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 breathlessness due to a lack of red blood cells (anaemia).

You may also have general symptoms such as unexplained weight loss, no appetite or feeling extremely tired.

How common is CUP?

CUP is the eighth most common cancer in Australia. It is the seventh most common cancer in women and the ninth most common in men. There are nearly 3,000 new cases of CUP diagnosed each year in Australia. It is more common in men than women and the risk increases with age.

Reviewed: Prof Martin Tattersall, Professor in Medicine, University of Sydney; Jane Barrett, CUP Survivor; David Currow, CEO of Cancer Institute NSW; Nadine Hackl, Cancer Institute NSW; A/Prof Chris Karapetis, Medical Oncologist, Flinders Medical Centre; Sylvie Lambert, Hunter Medical Research Institute, Post-doctoral Fellow; Monica Robotin, Medical Director, Cancer Council NSW; A/Prof Penelope Schofield, Supportive Care Research Group, Peter Mac; and A/Prof Claire Vajdic PhD, Lowy Cancer Research Centre, University of New South Wales.
 

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