Cancer of Unknown Primary Site

Understanding Your Condition



Cancer of unknown primary (CUP) is diagnosed when a patient has been found to have a secondary cancer (which may be in a number of sites including lymph glands, the liver, lungs or abdomen), but it is not possible to find where it has come from (the primary tumour).

Normally investigations will quickly reveal the original site of the cancer, but in a surprising number of cases (probably around 3%) there is no sign of a primary. This may be because the primary tumour is very small, or because it is in an area which does not show up well on imaging tests, or even because the primary cancer has genuinely disappeared either because it has been shed into the bowel or attacked by the body’s immune system.



CUP can present in many different ways depending on where the cancer has spread to. A biopsy is usually the most helpful test. This is a needle sample of the tumour, often taken by a radiologist with the assistance of ultrasound or CT guidance. The tumour will be looked at by a pathologist under the microscope and a number of special tests called immunohistochemistry tests will often give information to guide further tests. These may include blood tests for specific tumour markers, scans (usually CT and/or PET scans) or other tests to look for specific cancer such as mammograms or endoscopy. However if initial tests do not reveal an obvious diagnosis it may be better to initiate treatment rather than to have many more tests to find the primary cancer which may not take the diagnosis further, but can cause a significant delay in starting therapy.

A number of commercial companies produce “molecular diagnostics” which look in more detail at the genetic profile of the cancer using a variety of different techniques to try and identify the tissue of origin, but these tests are expensive and at the moment it is not clear how much information they add to standard diagnostic tests.



Unfortunately by the time a cancer has spread, with some specific exceptions it is usually not possible to cure, although some patients may respond very well to treatment. The management therefore is aimed at improving symptoms and quality of life and, if possible controlling the spread of the cancer for as long as possible. If patients with CUP are fit enough they may benefit from chemotherapy. This will normally be with a combination of drugs tailored to give the best possible chance of response, and will depend on the results of the biopsies, blood tests and imaging. Radiotherapy can be useful if the disease is confined to a single location, or is causing symptoms in a particular area. Surgery is rarely used in CUP, but on occasion can be considered again particularly if there is a single site of disease.

Cambridge Oncology Partners are happy to advise on the most appropriate investigations to perform in a patient with cancer of unknown primary, and we offer a full range of chemotherapy treatments. Radiotherapy if necessary is undertaken at Addenbrooke’s Hospital.


Useful links

Macmillan: Unknown Primary Site

Cancer Research UK: Unknown Primary Site

Cancer of Unknown Primary Site Foundation