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Cancer of unknown primary

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Radiation therapy for cancer of unknown primary

Radiation therapy uses high-energy rays or particles to destroy cancer cells. Radiation may be used for cancer of unknown primary (CUP):

  • as the primary treatment
    • Radiation therapy may be used to treat some people with squamous cell carcinoma in lymph nodes in the neck (cervical lymph nodes) or in the groin (inguinal lymph nodes).
  • with surgery or chemotherapy to try to shrink a tumour, destroy any cancer cells left behind after treatment or reduce the risk of cancer recurring
    • Radiation therapy to the breast may be used after lymph nodes are removed from under the arm.
    • Radiation therapy may be given after lymph nodes in the neck or groin are removed.
  • to relieve pain or control symptoms of advanced CUP (palliative radiation therapy)
    • Radiation therapy can help to relieve symptoms, such as pain, bleeding or trouble breathing. It may also be used to treat symptoms of bone metastases.

The amount of radiation given during treatment, and when and how it is given, will be different for each person. The type of radiation therapy treatment given will depend on the part of the body being treated and whether radiation therapy is being used to relieve symptoms or control and treat the cancer. Treatment may last from a few days to a few weeks. Sometimes only a single treatment may be given.

External beam radiation therapy

In most cases, CUP is treated with external beam radiation therapy. A machine directs radiation to the tumour and some of the surrounding tissue.


Brachytherapy is internal radiation therapy. A radioactive substance (radioactive isotope) is placed right into, or very close to, the tumour. Radioactive substances can also be placed in the area from where the tumour was removed. The radiation kills the cancer cells over time.

Brachytherapy may sometimes be used to treat certain symptoms of advanced CUP. For example, it might be used to help relieve a blockage in the large airways or treat symptoms like shortness of breath and cough.

See a list of questions to ask your doctor about radiation therapy.


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