This information is about unknown primary tumours (UPTs), which are also sometimes called an occult primary malignancy (OPM). It is only natural to be in a state of shock when you have been diagnosed with cancer. It is all the harder to accept when doctors do not seem to be able to identify where the cancer is. This is a fairly rare situation, but one which can cause a lot of distress.

A malignant tumour (cancer) is made up of millions of cancer cells. Some of these cells may break away from the original (primary) tumour, and spread to other parts of the body where they may form new tumours. These new tumours are referred to as metastases, or secondary tumours.

The secondary cancer is usually made up of exactly the same type of cancer cells as the primary cancer. This means, for example, that if someone has primary lung cancer that has spread to form secondary tumours in the bones, these bone secondaries will be made up of lung cancer cells. These are quite different from the abnormal bone cells that would form a primary bone cancer. The treatment used for these secondary bone cancers would be designed to treat lung cancer cells, not bone cancer cells.

Some secondary tumours, however, are made up of cells which cannot be identified under the microscope because they look too abnormal, and so it is not possible to tell what kind of a primary cancer they have come from.

For most people who have cancer, the primary cancer is easy to identify, as their symptoms will have alerted their doctor to the likely cause, and this will have been confirmed by the tests done at the hospital.

In people with an unknown primary tumour, the tests will have found evidence of a secondary cancer but will not have been able to identify the site of the primary cancer.

There are a number of possible reasons for why the primary might not have been found:

• The primary tumour may have disappeared spontaneously because your immune system may have destroyed the primary tumour, but not the secondaries.
• The secondaries may have grown and spread very quickly, while the primary is still too small to be seen on x-rays or scans.
• The primary tumour may be impossible to see on x-rays or scans because it is hidden by several larger secondaries that have grown close to it.
• It is thought that sometimes tumours of the lining of the digestive system may have been passed out of the body through the bowel.

Your doctor may want to do a number of tests in order to try to identify the primary cancer. Exactly which tests you will be asked to have will depend on the clues the doctor has already picked up – for example, the symptoms you have had, your medical history, and where your secondary cancer is. Unfortunately, it is not possible to describe here all the possible tests that you may be asked to consider. Your doctor, however, should describe to you the purpose of each test.

Tests will probably include an x-ray and a CT scan, blood tests, urine tests and a biopsy (the removal of a small sample of the secondary tumour for examination in the laboratory).

Although it can sometimes be helpful, there is often no real benefit in finding out where the primary cancer started. Your doctors will carefully choose only those tests they feel are absolutely necessary, rather than put you through lots of investigations and tests that may take time and be very tiring, but not make a difference to your overall care.

Information can help to reduce your frustration. Ask your doctor or the other staff looking after you to explain what the tests you are having involve, why they are being done, and what the results mean. If you don't understand their explanation at first, ask again. You may find it helpful to write down the questions you want to ask.

Some types of secondary cancers from unknown primaries are responsive to treatment, and you may be offered chemotherapy, hormonal therapy or radiotherapy, alone or in combination.

Unfortunately, for many people with an unknown primary tumour, by the time it is diagnosed, treatment is unlikely to bring about a cure. If you are feeling well when the cancer is diagnosed, and do not have any troublesome symptoms, your doctor may initially suggest no treatment. This is because it may be better to wait until you really need the treatment. This is not because nothing more can be done, but because the risks and side effects of any treatment outweigh the possible benefits at that time. Your doctor or specialist nurse can discuss this with you further.

Many drugs and other treatments are available to control your symptoms and make you feel more comfortable. These are known as palliative treatments or supportive care. If you have pain, sickness (nausea), or any other distressing symptoms, tell your doctor, or the nurse looking after you, so that they can offer you help and support.

You may want to try a complementary therapy, such as relaxation, visualisation or aromatherapy, which can help to relieve tension and give you back a sense of being in control.

Many different emotions may affect you at this time. Anger, resentment, guilt, anxiety and fear of the unknown are some of the most common feelings that people may have. You may find yourself tearful, restless and unable to sleep. You may experience feelings of hopelessness and depression. These are all normal reactions, but it is often difficult and distressing to admit to them.

You do not have to cope with these feelings on your own; there are people available to help you. Some hospitals have their own emotional support services with specially trained staff, and many of the nurses on the ward will have been given training in counselling. You may feel more comfortable talking to a counsellor outside the hospital environment or to a religious leader.

This section has been compiled using information from a number of reliable sources including:

• Oxford Textbook of Oncology (2nd edition). Eds Souhami et al. Oxford University Press, 2002.
• Cancer and its Management (4th edition). Eds Souhami and Tobias. Oxford Blackwell Scientific Publications, 2003.
• The Textbook of Uncommon Cancers (2nd edition). Eds Raghavan et al. Wiley, 1999.

For further references, please see the general bibliography.