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Unknown primary

What is cancer of unknown primary?

Cancer occurs when abnormal cells within the body grow in an uncontrolled way. Cancer can form in any of the body’s tissues. The first cancer that develops is called the primary cancer. Cancer can then spread elsewhere in the body. When cancer spreads to another part of the body, this is called the secondary cancer.

Sometimes, the secondary cancer is found but the primary cancer cannot be found. This is called cancer of unknown primary.1

Why might it not be possible to find the primary cancer?

There are a number of reasons why it may not be possible to find the primary cancer.1

  • The primary cancer may be too small to be easily detected.
  • The body’s immune system may have killed the primary cancer.
  • The primary cancer may already have been removed by surgery for another condition.

What are the symptoms of cancer of unknown primary?

Symptoms of cancer of unknown primary vary depending on where the cancer has spread in the body.

Symptoms may include:

  • a lump or thickening in any part of the body1
  • a new or unusual pain that doesn’t go away1
  • a cough or hoarseness of the voice that doesn’t go away1
  • change in bladder habits (such as more frequent urination) or change in bowel habits (such as constipation or diarrhoea) 1
  • unusual bleeding or discharge1
  • unexplained fever that doesn’t go away1
  • night sweats1
  • loss of appetite or unexplained weight loss.1

There are a number of conditions that may cause these symptoms, not just cancer. If any of these symptoms are experienced, it is important that they are discussed with a doctor.

How is cancer of unknown primary diagnosed?

A number of tests may be performed to investigate symptoms that might be cancer and to try and find out where the primary cancer is.

Some of the tests used to investigate symptoms of cancer include:

  • a physical examination1
  • examination of a blood sample1
  • examination of a urine and/or stool sample1
  • a chest X-ray1
  • a mammogram
  • taking a sample of an unusual area of tissue (biopsy) for examination under a microscope.1

If these tests confirm that cancer is present, imaging tests, such as X-ray, ultrasound, computed tomography (CT) scan, magnetic resonance imaging (MRI), positron emission tomography (PET) scan may be used to look at different parts of the body.1

An internal examination may also be conducted using an endoscope – a thin flexible tube with a light on the end.1

Treatment options

Treatment and care of people with cancer is usually provided by a team of health professionals – called a multidisciplinary team.

Treatment for cancer of unknown primary depends on the stage of the disease, the severity of symptoms and the person’s general health. Treatment options can include surgery to remove tissue affected by cancer, radiotherapy, chemotherapy and/or hormonal therapy.1

Research is ongoing to find new ways to diagnose and treat different types of cancer. Some people may be offered the option of participation in a clinical trial to test new ways of treating cancer of unknown primary.

Finding support

People often feel overwhelmed, scared, anxious and upset after a diagnosis of cancer. These are all normal feelings.

Having practical and emotional support during and after diagnosis and treatment for cancer is very important. Support may be available from family and friends, health professionals or special support services.

More information about finding support can be found on this website: Living with cancer. This information deals with some of the challenges experienced by people affected by cancer. It includes information about managing some of the longer term side effects of treatment, how people close to you might feel after a diagnosis of cancer, and where to find practical and emotional support.

Cancer support organisations

In addition, State and Territory Cancer Councils provide general information about cancer as well as information on local resources and relevant support groups. The Cancer Council Helpline can be accessed from anywhere in Australia by calling 13 11 20 for the cost of a local call. Click here for a list of Cancer Councils and other cancer support organisations.


While Cancer Australia develops material based on the best available evidence, this information is not intended to be used as a substitute for an independent health professional’s advice. Cancer Australia does not accept any liability for any injury, loss or damage incurred by use of or reliance on the information contained in this document.


  1. National Cancer Institute. Carcinoma of unknown primary treatment (PDQ) – patient version. Available from http://www.cancer.gov/cancertopics/pdq/treatment/unknownprimary /Patient. [Accessed July 2012].