of Carcinoma of Unknown Primary

Carcinoma of unknown primary (CUP) is a rare disease in which 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. Cancers historically have been named based on their primary site of origin, regardless of where in the body they have spread. For example, a breast cancer that spreads to the liver is still classified as breast cancer and not as liver cancer.

Sometimes it’s not clear where a cancer may have started. When cancer is found in one or more metastatic sites but the primary site cannot be determined, it is called a CUP.  In many cases, the source of the cancer is never determined. Even the most thorough search may not find the primary site.

The main reason to look for the primary site of a CUP is to guide treatment. Since a cancer that starts in one place needs the same treatments when it spreads, knowing where a cancer started tells the doctor what types of treatments to use. This is especially important for certain cancers that respond well to specific chemotherapy or hormone drugs. When the types of cancer with the best hope for responding to treatment have been ruled out by certain tests, it usually becomes less important to find the exact origin or cancer type.

But even if the primary site is not known, treatment can still be successful. How the cancer looks under the microscope, the results of lab and genomic tests, and information about which organs it has already affected can help doctors predict what kinds of treatment might be helpful.1,2

Results of a recent clinical study suggest that a liquid biopsy to perform genomic analyses is feasible and that most patients with a CUP will have a unique genetic profile that can be treated with currently available precision cancer medicines.3

Next: Signs & Symptoms of CUP

Next: Diagnosis & Tests for CUP


1 Stella, GM; Senetta, R; Cassenti, A; Ronco, M; Cassoni, P (24 January 2012). “Cancers of unknown primary origin: current perspectives and future therapeutic strategies”. Journal of translational medicine. 10: 12.

2 National Institute for Health and Clinical Excellence. Clinical guideline 104: Metastatic malignant disease of unknown primary origin. London, 2010.

3 http://cancerres.aacrjournals.org/content/77/16/4238