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

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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:

  • Histologic study: A laboratory test in which stains are added to a sample of cancer cells or tissue and viewed under a microscope to look for certain changes in the cells. Certain changes in the cells are linked to certain types of cancer.
  • Immunohistochemistry study: A laboratory test in which dyes or enzymes are added to a sample of cancer cells or tissue to test for certain antigens (proteins that stimulate the body's immune response).
  • Reverse transcription–polymerase chain reaction (RT-PCR) test: A laboratory test in which cells in a sample of tissue are studied using chemicals to look for certain changes in the genes.
  • Cytogenetic analysis: A laboratory test in which cells in a sample of tissue are viewed under a microscope to look for certain changes in the chromosomes. Changes in certain chromosomes are linked to certain types of cancer.
  • Light and electron microscopy: A laboratory test in which cells in a sample of tissue are viewed under regular and high-powered microscopes to look for certain changes in the cells.

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.

  • When cancer is found above the diaphragm (the thin muscle under the lungs that helps with breathing), the primary cancer site is likely to be in the upper part of the body, such as in the lung or breast.
  • When cancer is found below the diaphragm, the primary cancer site is likely to be in the lower part of the body, such as the pancreas, liver, or other organ in the abdomen.
  • Some cancers commonly spread to certain areas of the body. For cancer found in the lymph nodes in the neck, the primary cancer site is likely to be in the head or neck, because head and neck cancers often spread to the lymph nodes in the neck.
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