Cancer of unknown primary

Thursday 1 May, 2014

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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? | Key points


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 it is not clear 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?

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

  • The secondary tumours may have grown and spread quickly, but the primary tumour is still too small to be seen on scans.
  • Your immune system has destroyed the primary tumour, but not the secondary tumours (metastases).
  • The primary tumour cannot be seen on x-rays, scans or endoscopies because it is hidden by secondaries that have grown close to it.

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 can be 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 the number of tests needed. They will only suggest tests they feel are necessary. Ask your doctor or nurse to explain the tests and how they’ll impact on your care, as this information can help you make an informed decision about having the tests.

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 the breast, colon, prostate, stomach, pancreas, liver and lungs.
  • 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 primary 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, being obese and certain infections. 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 more common than many people realise.

It 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 3000 new cases of CUP diagnosed each year in Australia.

Key points

  • CUP, or cancer of unknown primary, is a cancer that has spread from somewhere else in the body, but it’s not clear where in the body it started. The secondary cancer or secondaries can be identified, but not the primary.
  • It is also called occult primary cancer, tumour of unknown origin or metastatic malignancy of unknown primary.
  • It may not be possible to find the primary cancer because the secondary tumours have grown and spread quickly, but the primary tumour is still too small to be seen on scans. Or the primary cancer may have been destroyed by the immune system or is hidden by secondaries that have grown close to it.
  • Doctors will try to find the primary because it helps them decide what treatment to recommend.
  • Your doctor may ask you to have several tests to try to find the primary cancer.
  • Some people with CUP feel too unwell to have lots of tests.
  • Symptoms of CUP are often related to the area where the secondary cancer is found, and may include shortness of breath, bone pain and/or back pain, swelling and discomfort in the abdomen, and swollen lymph nodes in the neck, underarm, chest or groin.
  • If the tests cannot find where the cancer started, the doctor will try to identify the type of cell the cancer developed from. This information gives doctors a clue as to where the cancer started.
  • CUP is the eighth most common cancer in Australia. 

Reviewed by: A/Prof Linda Mileshkin, Consultant Medical Oncologist, Division of Cancer Medicine, Peter MacCallum Cancer Centre, VIC; Karen Hall, Nurse Counsellor, Helpline, Cancer Council SA and Clinical Nurse, Oncology/Haematology Inpatient Unit, Flinders Medical Centre, SA; A/Prof Chris Karapetis, Director of Clinical Research, Medical Oncologist, Flinders Centre for Innovation in Cancer, SA; A/Prof Claire Vajdic, Team Leader, Cancer Aetiology and Prevention Group, Prince of Wales Clinical School, Lowy Cancer Research Centre, University of NSW, NSW; and Robyn Wagner, Consumer. 

Updated: 01 May, 2014