Carcinoma of Unknown Primary

Carcinoma of Unknown Primary (CUP)

Carcinoma of unknown primary is cancer whose site of origin is not known.

Normally every cancer has a site of origin. For example, lung cancer is cancer that starts in the lung and then spreads to other parts of the body. A breast cancer is a cancer that starts in the breast and can spread to other parts of the body. A breast cancer that has spread to the liver for example, is not a liver cancer but a breast cancer in the liver. A liver cancer would be a cancer that starts in the liver itself and doesn’t come from anywhere else.

A CUP is a cancer where its site of origin is not known, and this can be a problem.

Why is it important to know the primary site of origin?

Every cancer, depending on its site of origin behaves differently and all treatment strategies are based on the type of cancer. Again, for example, breast cancer in the liver is treated differently to lung cancer in the liver. Hence, it is very important to determine the site of origin of any cancer before treatment is planned.

Why is it not possible to find a site of origin in some patients?

Finding a primary site can be difficult in some patients. By the time the patient is found to have cancer, it would have spread to multiple areas in the body and so, doctors may be unsure as to where it started. A lot of times, the primary site is obvious in that setting, but sometimes it isn’t.

What tests are done when Carcinoma of Unknown primary is diagnosed?

A range of tests can be done in a patient with carcinoma of unknown primary to find out the site of origin


Various scans can be done including a CT scan, PET-CT scan or an MRI scan. A PET-CT scan is commonly done and is good in being able to give an answer.

Blood Tests

Blood tests are done which may be able to determine the type of cancer. Specific blood tests such as tumour markers also help


A biopsy and examination of a cancer will help in identifying the source of the cancer. When the biopsy specimen is tested, special tests on the sample such as immunohistochemistry (IHC) is done and these tests can help to identify the primary site. Sometimes, IHC tests may give an idea of the primary but may not be sure about it. Occasionally, genetic testing on the biopsy sample may help in the diagnosis.

How is Carcinoma of Unknown Primary treated?

Usually, in the setting of a Cancer of unknown primary, the disease would have spread to different parts of the body making it stage 4 disease. Therefore, the treatment strategy will consist of treatment such as chemotherapy which will be able to go to all parts of the body and help control the cancer. If a site of origin of cancer is found in a patient, then treatment is planned based on the type of tumor found. A lot of times, despite a number of tests and scans, the primary site of origin is not known and then a “broad-based” treatment approach is used to cover many possibilities. Other treatments such as Radiotherapy are also used to control specific symptoms.