Carcinoma of unknown primary


Carcinoma of unknown primary is a diagnosis given when doctors aren't able to locate where a cancer began.

Most often, cancer is diagnosed when doctors discover the spot where the cancer began (primary tumor). If the cancer has spread (metastasized), those sites might be discovered, too.

In carcinoma of unknown primary, also known as occult primary cancer, doctors find the cancer cells that spread in the body, but they can't find the primary tumor.

Doctors consider the location of the primary tumor when choosing the most appropriate treatments. So if carcinoma of unknown primary is found, doctors work to try to identify the primary tumor site. Your doctor might consider your risk factors, symptoms, and results from exams, imaging tests and pathology tests when trying to determine where your cancer began.


Signs and symptoms of carcinoma of unknown primary depend on what part of the body is involved. In general, they might include:

  • A lump that can be felt through the skin
  • Pain
  • Changes in bowel habits, such as new and persistent constipation or diarrhea
  • Frequent urination
  • Cough
  • Fever
  • Night sweats
  • Losing weight without trying


In general, cancer forms when cells develop changes (mutations) in their DNA. The DNA contains instructions that tell cells what to do. Certain mutations can cause a cell to multiply uncontrollably and to continue living when normal cells would die. When this happens, the abnormal cells accumulate and form a tumor. The tumor cells can break away and spread (metastasize) to other parts of the body.

In carcinoma of unknown primary, the cancer cells that spread to other parts of the body are found. But the original tumor isn't found.

This can happen if:

  • The original cancer is too small to be detected by imaging tests
  • The original cancer was killed by the body's immune system
  • The original cancer was removed in an operation for another condition

Risk factors

The risk of carcinoma of unknown primary might be related to:

  • Older age. This type of cancer is most likely to occur in people older than 60.
  • Family history of cancer. There's some evidence that carcinoma of unknown primary might be associated with a family history of cancer that affects the lungs, kidneys or colon.


Tests and procedures used to diagnose carcinoma of unknown primary include:

  • Physical exam. Your doctor might ask you about your signs and symptoms and examine the area that concerns you to gather clues about your diagnosis.
  • Imaging tests. You might have imaging tests, such as X-ray, CT or MRI, to help with your diagnosis.
  • Removing a sample of tissue for testing. To confirm that your symptoms are caused by cancer, your doctor may recommend a procedure to remove a sample of cells for lab testing (biopsy). This might be done by inserting a needle through your skin, or you might need an operation. In the lab, doctors will analyze the cells to see if they're cancerous and where they might have originated.

Tests to look for the original cancer

If initial tests find cancer cells that came from somewhere else in the body, you might have additional tests to look for the place where the cancer cells originated (primary tumor).

Tests might include:

  • Physical exam. Your doctor will carefully examine your body to look for signs of cancer.
  • Imaging tests. Your doctor might recommend imaging tests to look for signs of the original cancer. These tests might include CT and positron emission tomography (PET) scans.
  • Blood tests. Blood tests that measure your organ function can give your doctor clues about whether cancer might be affecting your organs, such as your kidneys and liver. Blood tests that look for molecules that are sometimes produced by certain types of cancer (tumor markers) might provide more information for your diagnosis. Examples of tumor markers include prostate-specific antigen (PSA) for prostate cancer and cancer antigen (CA) 125 for ovarian cancer.
  • Using a scope to examine the inside of the body. The doctor might use a long thin tube equipped with a camera to examine the inside of your body to look for signs of cancer. The scope might be passed through your mouth to examine the inside of your lungs, esophagus, stomach, liver or small intestine. To examine the colon and rectum, the scope can be inserted through your anus.
  • Advanced lab testing. Doctors who specialize in analyzing blood and body tissue (pathologists) might run more-thorough tests of your cancer cells to gather more information for your diagnosis. Pathologists might use high-tech microscopes, special dyes and other technology, such as tests to look for changes in the genes and chromosomes of the cancer cells' DNA.

These tests might help your doctor locate the primary tumor where your cancer started. If the primary tumor is found, you would no longer have carcinoma of unknown primary. If your primary tumor can't be located despite testing, the results from these tests will help your doctor determine which treatments are most likely to help you.


To determine which treatments might be best for you, your doctor will consider where your cancer cells were found, which type of normal cells they most closely resemble and the results of lab tests. The treatment plan is personalized to your particular clinical situation and your personal preferences.

Treatments might include:

  • Chemotherapy. Chemotherapy uses drugs to kill cancer cells. One or more chemotherapy drugs may be given through a vein in your arm (intravenously), taken orally, or administered with both methods. Chemotherapy might be recommended if you have cancer cells in more than one area.
  • Radiation therapy. Radiation therapy uses high-powered energy beams from sources such as X-rays and protons to kill cancer cells. During radiation therapy, you lie on a table while a machine moves around you, directing radiation to precise points on your body. Radiation therapy might be used for carcinoma of unknown primary that's limited to one area of the body. It can also be used to help control symptoms, such as a growing cancer that's causing pain.
  • Surgery. An operation to cut away the cancer might be an option if your carcinoma of unknown primary is limited to one area, such as a lymph node or the liver. Your doctor might recommend radiation after surgery to kill any cancer cells that might remain.
  • Supportive (palliative) care. Palliative care is specialized medical care that focuses on providing relief from pain and other symptoms of a serious illness. Palliative care specialists work with you, your family and your other doctors to provide an extra layer of support that complements your ongoing care. Palliative care can be used while undergoing other aggressive treatments, such as surgery, chemotherapy or radiation therapy.

Coping and support

A diagnosis of carcinoma of unknown primary can be distressing because of the uncertainty that comes with it. You may undergo many tests and still not know exactly where your cancer began.

With time, you'll find what helps you cope with the uncertainty and distress. Until then, you may find that it helps to:

  • Learn enough about cancer to make decisions about your care. Ask your doctor about your cancer, including your test results, treatment options and, if you like, your prognosis. As you learn more about cancer, you may become more confident in making treatment decisions.
  • Keep friends and family close. Keeping your close relationships strong will help you deal with your cancer. Friends and family can provide the practical support you'll need, such as helping take care of your home if you're in the hospital. And they can serve as emotional support when you feel overwhelmed by cancer.
  • Find someone to talk with. Find a good listener who is willing to hear you talk about your hopes and fears. This may be a friend or family member. The concern and understanding of a counselor, medical social worker, clergy member or cancer support group also may be helpful.

    Ask your doctor about support groups in your area. Other sources of information include the National Cancer Institute and the American Cancer Society.

Preparing for an appointment

Make an appointment with your doctor if you have any signs or symptoms that worry you. If your doctor suspects that you might have cancer, you may be referred to a doctor who specializes in caring for people with cancer (oncologist).

Here's some information to help you get ready for your appointment.

What you can do

When you make the appointment, ask if there's anything you need to do in advance, such as fasting before having a specific test. Make a list of:

  • Your symptoms, including any that seem unrelated to the reason for your appointment
  • Key personal information, including major stresses, recent life changes and family medical history
  • All medications, vitamins or other supplements you take, including the doses
  • Questions to ask your doctor

Consider bringing a family member or friend to help you remember the information you're given.

For carcinoma of unknown primary, some basic questions to ask your doctor include:

  • What's likely causing my symptoms?
  • Other than the most likely cause, what are other possible causes for my symptoms?
  • What tests do I need?
  • What's the best course of action?
  • What are the alternatives to the primary approach you're suggesting?
  • I have other health conditions. How can I best manage them together?
  • Are there restrictions I need to follow?
  • Should I see a specialist?
  • Are there brochures or other printed material I can have? What websites do you recommend?

Don't hesitate to ask other questions.

What to expect from your doctor

Your doctor is likely to ask you several questions, such as:

  • When did your symptoms begin?
  • Have your symptoms been continuous or occasional?
  • How severe are your symptoms?
  • What, if anything, seems to improve your symptoms?
  • What, if anything, appears to worsen your symptoms?

Content From Mayo Clinic Updated: 10/05/2022
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