Carcinoma of unknown primary is a rare cancer diagnosis given when cancer has spread and the original site of the cancer is unknown. Treatment is based on what can be discovered and what’s the most likely type of cancer. Options include standard treatments and investigational drugs.
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Carcinoma of unknown primary (CUP) is a diagnosis given when cancer is found in your body but it’s not known where the original cancer started.
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Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy
Cancer can start in any tissue in your body. Where it first starts — the primary location — defines the cancer. In other words, if cancer begins in your liver and spreads (metastasizes) to your lung, it’s still called liver cancer and not lung cancer.
Cells of your tissues and organs have features that are unique to that tissue and other features that are shared by several tissue types. Features are things like the size and shape of the cells, their DNA and cell arrangement. Knowing various cell types helps doctors recognize healthy cells and cancer cells. Cancer changes the usual appearance of a cell type. Doctors can determine that cancer has spread when they find abnormal cell types in another part of your body where they don’t belong (for example, finding abnormal liver cells in your lung tissue).
Sometimes when cancer spreads to another area of your body and the abnormal cell features don’t lead to finding where cancer first started, the cancer is called carcinoma of unknown primary (CUP). It’s also known as occult primary tumor.
The primary cancer (cancer that first formed) may not be found because:
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Carcinoma of unknown primary is the diagnosis in about 2% of all cancers each year in the U.S.
There are no unique symptoms to carcinoma of unknown primary (CUP). If you notice any of these general signs and symptoms of cancer, see your healthcare provider:
Cancer can have many different causes. Pinpointing a particular cause of carcinoma of unknown primary is especially difficult because the original site of the cancer is not known.
In general, cancer is the result of changes in the DNA of cells. These abnormal cells then divide, multiply and possibly spread to areas in your body beyond where they started.
Your healthcare provider may first perform or order one or more of these standard tests:
If your healthcare provider finds a lump or your symptoms and initial round of tests indicate that you may have cancer, they will take a biopsy. During a biopsy, some cells or tissue are removed from your body (gathered in a needle through your skin or during an operation) so they can be looked at under a microscope.
A pathologist (a doctor who examines cells) uses different kinds of high-powered microscopes and dyes, stains or chemicals to make cell details easier to see and to look for changes in the DNA of cells. Certain cell changes or details are linked to certain types of cancers.
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Several types of scans and other tests or procedures may be used, including:
Normally, cancers are staged based on the extent of how far they spread in your body. Carcinoma of unknown primary (CUP) has already spread to other areas of your body when it’s found. Because it’s not known where the cancer began or how long it’s been present, there’s no staging system for CUP.
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Since there’s no staging for carcinoma of unknown primary (CUP) because it has already spread and the primary cancer site may not be known, your healthcare provider plans treatment based on what is known and what is thought to be the most likely type of cancer.
Your healthcare team will consider where the cancer was found in your body, what type of original cells the cancer cells look like, how abnormal the cells look and your test results.
Treatments usually considered include:
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Your healthcare providers will also provide pain relief and other treatments to manage your symptoms.
Carcinoma of unknown primary (CUP) that recurs is usually treated within a clinical trial with an investigational drug. Your healthcare team will determine where in your body cancer has returned, the type of cancer it is and how it was treated before. You and your healthcare team will decide the treatment option that is best for you.
Clinical trials enroll people from all points in their plan of care — before, during or after starting standard treatment approaches. People involved in cancer clinical trials receive either a standard treatment or a new treatment. Neither you nor your healthcare professional knows which treatment you’re receiving.
Clinical trials are done to find out if the new drug is safe and effective or even better than the standard treatment. All drugs approved for use in the U.S. must have undergone clinical trials. Talk with your healthcare team to discuss if this is a good treatment choice for you.
Like other cancers, certain risk factors can increase your risk of cancer. However, having or not having risk factors doesn’t guarantee that you will or won’t get cancer. Still, known cancer risks that you can act on to improve your general health and perhaps lower your risk of cancer include:
Because carcinoma of unknown primary (CUP) is not the primary cancer and has already spread when it was found, the potential to cure the cancer is less likely than finding a primary cancer early. Survival rates vary from person to person, ranging from months to several years. Life expectancy depends on factors that affect outcomes including:
A note from Cleveland Clinic
Hearing news that you have cancer is scary. Know that your healthcare team is with you. They will perform the needed tests and scans to develop and create the best possible treatment plan. Keep in mind that there’s always hope and that survival statistics are based on large numbers of people who had the disease. What might happen in your case is unique to you. Also know that many treatments for cancer are available and many investigational drugs can be tried through a clinical trial. Don’t hesitate to discuss your concerns, fears and prognosis with your team. Not only can they be a source of knowledge, comfort and support, they can also direct you to other healthcare professionals skilled in coping with stress and anxiety that often come with a diagnosis of cancer and can help you find local support groups.
Last reviewed on 06/24/2021.
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