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This information is produced and provided by the National Cancer Institute (NCI). The information in this topic may have changed since it was written. For the most current information, contact the National Cancer Institute via the Internet web site at http://cancer.gov or call 1-800-4-CANCER.
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. In carcinoma of unknown primary, cancer cells have spread in the body but the place where the primary cancer began is unknown.
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.
There is no staging system for carcinoma of unknown primary (CUP).
The extent or spread of cancer is usually described as stages. The stage of the cancer is usually used to plan treatment. However, CUP has already spread to other parts of the body when it is found.
The information that is known about the cancer is used to plan treatment.
Doctors use the following types of information to plan treatment:
There are different types of treatment for patients with carcinoma of unknown primary (CUP).
Different types of treatment are available for patients with CUP. Some treatments are standard (the currently used treatment), and some are being tested in clinical trials. A treatment clinical trial is a research study meant to help improve current treatments or obtain information on new treatments for patients with cancer. When clinical trials show that a new treatment is better than the standard treatment, the new treatment may become the standard treatment. Patients may want to think about taking part in a clinical trial. Some clinical trials are open only to patients who have not started treatment.
Four types of standard treatment are used:
Surgery is a common treatment for CUP. A doctor may remove the cancer and some of the healthy tissue around it.
After the doctor removes all the cancer that can be seen at the time of the surgery, some patients may be given chemotherapy or radiation therapy after surgery to kill any cancer cells that are left. Treatment given after the surgery, to lower the risk that cancer will come back, is called adjuvant therapy.
Radiation therapy is a cancer treatment that uses high-energy x-rays or other types of radiation to kill cancer cells or keep them from growing. There are two types of radiation therapy:
The way the radiation therapy is given depends on the type and stage of the cancer being treated. External and internal radiation therapy are used to treat carcinoma of unknown primary.
Chemotherapy is a cancer treatment that uses drugs to stop the growth of cancer cells, either by killing the cells or by stopping them from dividing. When chemotherapy is taken by mouth or injected into a vein or muscle, the drugs enter the bloodstream and can reach cancer cells throughout the body (systemic chemotherapy). When chemotherapy is placed directly into the cerebrospinal fluid, an organ, or a body cavity such as the abdomen, the drugs mainly affect cancer cells in those areas (regional chemotherapy). Combination chemotherapy is the use of two or more anticancer drugs.
Hormone therapy is a cancer treatment that removes hormones or blocks their action and stops cancer cells from growing. Hormones are substances made by glands in the body and circulated in the bloodstream. Some hormones can cause certain cancers to grow. If tests show that the cancer cells have places where hormones can attach (receptors), drugs, surgery, or radiation therapy are used to reduce the production of hormones or block them from working.
New types of treatment are being tested in clinical trials.
Information about clinical trials is available from the NCI website.
Treatment for carcinoma of unknown primary may cause side effects.
For information about side effects caused by treatment for cancer, see our Side Effects page.
Patients may want to think about taking part in a clinical trial.
For some patients, taking part in a clinical trial may be the best treatment choice. Clinical trials are part of the cancer research process. Clinical trials are done to find out if new cancer treatments are safe and effective or better than the standard treatment.
Many of today's standard treatments for cancer are based on earlier clinical trials. Patients who take part in a clinical trial may receive the standard treatment or be among the first to receive a new treatment.
Patients who take part in clinical trials also help improve the way cancer will be treated in the future. Even when clinical trials do not lead to effective new treatments, they often answer important questions and help move research forward.
Patients can enter clinical trials before, during, or after starting their cancer treatment.
Some clinical trials only include patients who have not yet received treatment. Other trials test treatments for patients whose cancer has not gotten better. There are also clinical trials that test new ways to stop cancer from recurring (coming back) or reduce the side effects of cancer treatment.
Clinical trials are taking place in many parts of the country. Information about clinical trials supported by NCI can be found on NCI's clinical trials search webpage. Clinical trials supported by other organizations can be found on the ClinicalTrials.gov website.
For information about the treatments listed below, see the Treatment Option Overview section.
Newly Diagnosed Carcinoma of Unknown Primary
Cervical (Neck) Lymph Nodes
Cancer found in cervical (neck) lymph nodes may have spread from a tumor in the head or neck. Treatment of cervical lymph node carcinoma of unknown primary (CUP) may include the following:
See the PDQ summary on Metastatic Squamous Neck Cancer with Occult Primary Treatment (Adult) for more information.
Poorly Differentiated Carcinomas
Cancer cells that are poorly differentiated look very different from normal cells. The type of cell they came from is not known. Treatment of poorly differentiated carcinoma of unknown primary, including tumors in the neuroendocrine system (the part of the brain that controls hormone -producing glands throughout the body) may include the following:
Women with Peritoneal Cancer
Treatment for women who have peritoneal (lining of the abdomen) carcinoma of unknown primary may be the same as for ovarian cancer. Treatment may include the following:
See the PDQ summary on Ovarian Epithelial, Fallopian Tube, and Primary Peritoneal Cancer Treatment for more information.
Isolated Axillary Lymph Node Metastasis
Cancer found only in the axillary (armpit) lymph nodes may have spread from a tumor in the breast.
Treatment of axillary lymph node metastasis is usually:
Treatment also may include one or more of the following:
Inguinal Lymph Node Metastasis
Cancer found only in the inguinal (groin) lymph nodes most likely began in the genital, anal, or rectal area. Treatment of inguinal lymph node metastasis may include the following:
Melanoma in a Single Lymph Node Area
Treatment of melanoma that is found only in a single lymph node area is usually:
See PDQ summary on Melanoma Treatment for more information.
There is no standard treatment for carcinoma of unknown primary that is found in several different areas of the body. Treatment may include the following:
Recurrent Carcinoma of Unknown Primary
Treatment for recurrent carcinoma of unknown primary is usually within a clinical trial. Treatment depends on the following:
Use our clinical trial search to find NCI-supported cancer clinical trials that are accepting patients. You can search for trials based on the type of cancer, the age of the patient, and where the trials are being done. General information about clinical trials is also available.
For more information from the National Cancer Institute about carcinoma of unknown primary, see the following:
For general cancer information and other resources from the National Cancer Institute, see the following:
Physician Data Query (PDQ) is the National Cancer Institute's (NCI's) comprehensive cancer information database. The PDQ database contains summaries of the latest published information on cancer prevention, detection, genetics, treatment, supportive care, and complementary and alternative medicine. Most summaries come in two versions. The health professional versions have detailed information written in technical language. The patient versions are written in easy-to-understand, nontechnical language. Both versions have cancer information that is accurate and up to date and most versions are also available in Spanish.
PDQ is a service of the NCI. The NCI is part of the National Institutes of Health (NIH). NIH is the federal government's center of biomedical research. The PDQ summaries are based on an independent review of the medical literature. They are not policy statements of the NCI or the NIH.
Purpose of This Summary
This PDQ cancer information summary has current information about the treatment of carcinoma of unknown primary. It is meant to inform and help patients, families, and caregivers. It does not give formal guidelines or recommendations for making decisions about health care.
Reviewers and Updates
Editorial Boards write the PDQ cancer information summaries and keep them up to date. These Boards are made up of experts in cancer treatment and other specialties related to cancer. The summaries are reviewed regularly and changes are made when there is new information. The date on each summary ("Updated") is the date of the most recent change.
The information in this patient summary was taken from the health professional version, which is reviewed regularly and updated as needed, by the PDQ Adult Treatment Editorial Board.
Clinical Trial Information
A clinical trial is a study to answer a scientific question, such as whether one treatment is better than another. Trials are based on past studies and what has been learned in the laboratory. Each trial answers certain scientific questions in order to find new and better ways to help cancer patients. During treatment clinical trials, information is collected about the effects of a new treatment and how well it works. If a clinical trial shows that a new treatment is better than one currently being used, the new treatment may become "standard." Patients may want to think about taking part in a clinical trial. Some clinical trials are open only to patients who have not started treatment.
Clinical trials can be found online at NCI's website. For more information, call the Cancer Information Service (CIS), NCI's contact center, at 1-800-4-CANCER (1-800-422-6237).
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The best way to cite this PDQ summary is:
PDQ® Adult Treatment Editorial Board. PDQ Carcinoma of Unknown Primary Treatment. Bethesda, MD: National Cancer Institute. Updated <MM/DD/YYYY>. Available at: https://www.cancer.gov/types/unknown-primary/patient/unknown-primary-treatment-pdq. Accessed <MM/DD/YYYY>. [PMID: 26389238]
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Last Revised: 2019-10-23
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