Cancer of unknown primary

Cancer can begin anywhere in the body. The place where cancer first grows is called the primary cancer. If the primary

cancer spreads to grow in other parts of your body it is called advanced (secondary, metastatic or stage IV) cancer.

Cancer cells usually look like the cells in the place that the cancer first started. For example, breast cancer cells may

spread to the lungs. Because cancer began in the breast, the cancer cells in the lungs look like breast cancer



Sometimes, doctors find where cancer has spread to, but can’t find where it first began. This type of cancer is called cancer of unknown primary (CUP).


Why can’t the doctors find the primary cancer?

There are different reasons why a primary cancer can’t be found:

  • the primary cancer is very small
  • the body’s immune system killed the primary cancer
  • the cancer is in many parts of your body and it’s not clear which part was first affected
  • the primary cancer was removed during surgery for another condition and the doctors did not know the cancer was there. 

Symptoms of CUP

  • Signs and symptoms of CUP depend on where the cancer has spread. Some signs that may need to be checked include:
  • a lump on any part of your body
  • pain that is in one part of your body and does not go away
  • a cough that does not go away
  • change in bowel or bladder habits
  • fever for no reason that does not go away
  • night sweats
  • weight loss for no reason.

Tests used to find the primary cancer

Your treatment team will begin to find the reason for these symptoms by asking you questions about your health. They may also ask you to have some tests done to give them more information about the symptoms you are experiencing. 

The part of the body where the cancer cells are first found may help the doctor decide what tests will be most helpful. 

  • When cancer is found above the diaphragm (the muscle under the lungs that help with breathing), the primary cancer is likely to be in the upper part of the body such as the lung or breast.
  • When cancer is found below the diaphragm, the primary cancer is likely to be in the lower part of the body, such as the pancreas or liver.

The following tests may be done to find where the cancer first started: biopsy, blood tests, scans, mammograms, Endoscopy, and Tumour marker tests 


The spread of cancer is usually described in stages. The stage of the cancer is used to plan treatment. Because CUP has already spread to another part of the body when it is found, your doctors may describe the cancer as stage 3 or 4. They will use the following information to plan your treatment:

  • the place in your body that the cancer is found
  • the type of cancer cells
  • what the cancer cells look like
  • the signs and symptoms the cancer is causing
  • the results of any tests you have had
  • if the cancer is new or has come back.

Treatment for CUP

Because CUP is an advanced cancer, treatment is unlikely to cure the cancer.The aim of treatment is to control any symptoms caused by the cancer and to maintain or improve your quality of life. These are the typical treatments for CUP: chemotherapy, radiation treatment, hormone treatment and surgery.

Treatment may leave you feeling very tired.  You might feel sick, have diarrhoea and some people may lose their hair. Most of these side effects go away when treatments end.  Your treatment team will talk with you about any side affects you are likely to experience and how to manage them.

Some types of CUP respond to hormone treatment. Hormone treatment adds, blocks or removes hormones.  For women, hormone treatment may be used if the treatment team think the primary cancer site is the breast.  For men, it may be used if they think the prostate is the primary cancer site.

Surgery is used to help relieve symptoms caused by CUP, such as pain caused by the cancer pressing on organs or nerves. Some people have chemotherapy or radiation treatment after surgery to treat any cancer cells that are left. There are risks and side effects for any type of surgery. Your treatment team will let you know what to expect if you are having surgery.


Living with CUP

Advanced cancer can cause physical and emotional stress. You may be receiving treatments for the rest of your life. Cancer may go through cycles of growing, shrinking,or seem to disappear. In most cases, advanced cancer may change but it is unlikely to go away completely. For more information on living well with an advanced cancer diagnosis go here.

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