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General Information About Carcinoma of Unknown Primary

Carcinoma of unknown primary (CUP) is a rare disease in which malignant (cancer) cells are found in the body but the place the cancer began is not known.

Cancer can form in any tissue of the body. The primary cancer (the cancer that first formed) can spread to other parts of the body. This process is called metastasis. Cancer cells usually look like the cells in the type of tissue in which the cancer began. For example, breast cancer cells may spread to the lung. Because the cancer began in the breast, the cancer cells in the lung look like breast cancer cells.

Sometimes doctors find where the cancer has spread but cannot find where in the body the cancer first began to grow. This type of cancer is called a cancer of unknown primary (CUP) or occult primary tumor. Tests are done to find where the primary cancer began and to get information about where the cancer has spread. When tests are able to find the primary cancer, the cancer is no longer a CUP and treatment is based on the type of primary cancer.

Sometimes the primary cancer is never found.

The primary cancer (the cancer that first formed) may not be found for one of the following reasons:

The signs and symptoms of CUP are different, depending on where the cancer has spread in the body.

Sometimes CUP does not cause any signs or symptoms. Signs and symptoms may be caused by CUP or by other conditions. Check with your doctor if you have any of the following:

Different tests are used to detect (find) cancer.

The following tests and procedures may be used:

If tests show there may be cancer, a biopsy is done.

A biopsy is the removal of cells or tissues so they can be viewed under a microscope by a pathologist. The pathologist views the tissue under a microscope to look for cancer cells and to find out the type of cancer. The type of biopsy that is done depends on the part of the body being tested for cancer. One of the following types of biopsies may be used:

If cancer is found, one or more of the following laboratory tests may be used to study the tissue samples and find out the type of cancer:

When the type of cancer cells or tissue removed is different from the type of cancer cells expected to be found, a diagnosis of CUP may be made.

The cells in the body have a certain look that depends on the type of tissue they come from. For example, a sample of cancer tissue taken from the breast is expected to be made up of breast cells. However, if the sample of tissue is a different type of cell (not made up of breast cells), it is likely that the cells have spread to the breast from another part of the body. In order to plan treatment, doctors first try to find the primary cancer (the cancer that first formed).

Tests and procedures used to find the primary cancer depend on where the cancer has spread.

In some cases, the part of the body where cancer cells are first found helps the doctor decide which diagnostic tests will be most helpful.

The following tests and procedures may be done to find where the cancer first began:

Sometimes, none of the tests can find the primary cancer site. In these cases, treatment may be based on what the doctor thinks is the most likely type of cancer.

Certain factors affect prognosis (chance of recovery).

The prognosis (chance of recovery) depends on the following:

For most patients with CUP, current treatments do not cure the cancer. Patients may want to take part in one of the many clinical trials being done to improve treatment. Clinical trials for CUP are taking place in many parts of the country. Information about clinical trials is available from the NCI website.


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