Radiation Therapy for a Cancer of Unknown Primary

Radiation therapy uses high-energy rays (or particles) to kill cancer cells or slow their rate of growth. The goal of radiation therapy may change based on the situation.

For some cancers that have not spread too far from where they started, it can be used alone or with other treatments such as surgery with the goal of trying to cure the cancer.

When cancer has spread extensively, radiation can be used to relieve symptoms such as pain, bleeding, trouble swallowing, intestinal blockage, compression of blood vessels or nerves by tumors, and problems caused by metastases to bones.

  • External beam radiation therapy focuses a beam of radiation on the cancer from a machine
  • Internal radiation therapy (brachytherapy) places a radioactive material directly into or as close as possible to the cancer.

Internal radiation therapy lets your doctor give a dose of radiation to a smaller area and in a shorter time than is possible with external radiation treatment.

Sometimes, both internal and external beam radiation therapies are used together.

Possible side effects of radiation therapy

Depending on where the radiation is aimed or placed and what dose is given, side effects may include the following:

Possible general side effects from radiation

  • Fatigue (feeling tired)
  • Loss of appetite
  • Low blood counts
  • Skin changes in areas getting radiation, ranging from redness to blistering and peeling
  • Hair loss at the site where the radiation is aimed

Possible side effects from radiation to the head and neck

Radiation therapy to the head and neck area often causes damage to the throat and salivary glands, which can result in:

  • Throat pain
  • Mouth sores
  • Trouble swallowing
  • Loss of taste
  • Hoarseness
  • Dry mouth

Over the long term it can also lead to cavities in the teeth and thyroid problems (from damage to the thyroid gland). This might mean that you need pills to replace thyroid hormone.

Possible side effects from radiation to the chest

  • Trouble and pain swallowing from irritation of the esophagus (the tube that connects the throat to the esophagus
  • Lung irritation that can lead to cough and shortness of breath

Possible side effects from radiation to the abdomen

  • Nausea
  • Vomiting
  • Diarrhea
  • Poor appetite

Possible side effects from radiation to the pelvis

  • Bladder irritation, leading to symptoms like pain or burning with urination and feeling like you have to go often
  • Irritation of the rectum and anus, which can lead to diarrhea, bleeding, and pain
  • In women, vaginal irritation and discharge.

Most of these side effects go away after treatment ends, but some are long-term and may never go away completely.

If chemotherapy is given along with radiation, the side effects are often worse.

There are ways to relieve many of these side effects, so it’s important to discuss any changes you notice with your cancer care team.

For more detailed information, see the Radiation Therapy section of our website.

The American Cancer Society medical and editorial content team
Our team is made up of doctors and master's-prepared nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

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Last Medical Review: March 9, 2018 Last Revised: March 9, 2018

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