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Carcinoma of Unknown Primary Treatment (PDQ®): Treatment - Patient Information [NCI] - 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.

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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 primary cancer is very small and grows slowly.
  • The body's immune system killed the primary cancer.
  • The primary cancer was removed during surgery for another condition and doctors didn't know cancer had formed. For example, a uterus with cancer may be removed during a hysterectomy to treat a serious infection.

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:

  • Lump or thickening in any part of the body.
  • Pain that is in one part of the body and does not go away.
  • A cough that does not go away or hoarseness in the voice.
  • Change in bowel or bladder habits, such as constipation, diarrhea, or frequent urination.
  • Unusual bleeding or discharge.
  • Fever for no known reason that does not go away.
  • Night sweats.
  • Weight loss for no known reason or loss of appetite.
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