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Breast cancer

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Potential side effects of radiation therapy for breast cancer

Side effects can occur with any type of treatment for breast cancer, but not everyone has them or experiences them in the same way. Side effects of radiation therapy will depend mainly on the:

  • size of the area being treated
  • specific area or organs being treated
  • total dose
  • treatment schedule

Radiation therapy damages cancer cells, but healthy cells in the treatment area can also be damaged, even though steps are taken to protect them as much as possible. Different cells and tissues in the body tolerate radiation differently.

Side effects can happen any time during radiation therapy. Some may happen during, immediately after or a few days or weeks after radiation therapy. Most side effects go away after radiation therapy is completed. Late side effects can occur months or years after radiation therapy. Some side effects may last a long time or be permanent.

It is important to report side effects to the healthcare team. Many side effects can be relieved by medications, a change in diet or other measures. Doctors may also grade (measure) how severe certain side effects are. Sometimes radiation therapy treatments need to be adjusted if side effects are severe.

Because of some of the potential side effects of radiation therapy for breast cancer, it is usually suggested that women not wear a bra until after their radiation therapy treatments are completely finished. However, if this is too uncomfortable, talk to the radiation therapy team about possible options. They may suggest wearing a soft, comfortable bra without an underwire.


Fatigue is one of the most common side effects of radiation therapy for breast cancer. Fatigue may be caused by anemia, poor appetite or depression. It may also be related to toxic substances that are produced when cancer cells break down and die. During radiation therapy, the body uses more energy to heal itself, so fatigue will not always be relieved by rest. Making frequent, daily trips for radiation treatments can also be tiring.

Fatigue usually begins during the second week of treatment or later. Symptoms of fatigue may increase or become more severe over the course of treatment. Fatigue usually goes away gradually after treatment has ended, but some people continue to feel tired for several weeks or months after radiation treatment is finished.

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Skin reactions

Skin reactions occur because external beam radiation travels through the skin to reach the area being targeted for treatment. The skin in the radiated area may be:

  • red, darker or tanned looking
  • dry
  • itchy
  • tender or sore
    • The nipple and the fold under the breast can also become sore.
  • peeled or blistered
  • thicker
  • scarred
  • moist, weepy
  • broken (a sore)
  • speckled with tiny red marks where the blood vessels have broken (telangiectasia)

Most skin reactions occur within the first 2 weeks of receiving radiation treatment. They usually go away a few weeks after treatment. Some skin changes, like skin darkening, telangiectasia or scarring, can persist. Some women do not experience any skin reactions with radiation therapy.

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Changes to the breast

Radiation therapy can cause a number of different changes to the breast receiving treatment:

  • change in breast size, shape or firmness
    • Breast swelling may last up to 6 months after treatment has ended when radiation therapy is given after breast-conserving surgery.
  • changes in sensation (increased or decreased) in the treated area
  • soreness, heaviness, discomfort or tightness

Women should report to the healthcare team any new changes in the breast that occur several months after radiation treatments are finished. This may include changes in size, shape or appearance of the breast.

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Breast pain

Some women may have discomfort or pain in the breast being treated with radiation therapy. It usually lasts up to 6 months after radiation therapy is finished, but some women may continue to have pain for a longer period of time.

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Difficulty swallowing

Radiation therapy may cause the tissues of the throat and esophagus to become sore and inflamed. This causes pain and difficulty swallowing. This side effect usually starts 2–3 weeks after radiation treatment starts. It goes away when treatment ends and the inflammation decreases.

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Shoulder stiffness

After radiation therapy, some women may have difficulty moving their shoulder because the radiation causes changes to the muscles. Rehabilitation exercises may help people keep normal shoulder movement.

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Some women may have nausea during radiation therapy for breast cancer, but this is uncommon.

Nausea and vomiting can usually be managed with anti-nausea medication and usually go away after treatment is finished.

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Radiation pneumonitis

Radiation pneumonitis is an uncommon side effect of radiation therapy for breast cancer. It may occur a few weeks to several months after radiation treatment. It occurs more often in women who receive methotrexate and 5-fluorouracil (Adrucil, 5-FU) at the same time as radiation therapy.

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Nerve damage

Radiation therapy for breast cancer can damage the nerves in the arm (brachial plexopathy). Nerve damage can cause burning, numbness or tingling in the arm and hand. Nerve damage is uncommon, but it may be a long-term side effect in some women.

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Heart damage

The heart may be damaged if the left breast or left chest wall are treated with radiation therapy at the same time that chemotherapy is given. This is a rare, long-term side effect.

Report shortness of breath, swelling of the arms or legs or chest pain to the healthcare team. Heart function may be monitored to check for injury or damage to the heart. Medicines or other treatments may be needed for heart problems. Long-term follow-up is necessary if heart problems occur.

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Rib fractures

In rare cases, radiation therapy for breast cancer may cause damage to the bone cells in the ribs, which can lead to rib fractures.

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Second cancers

Second cancers caused by radiation therapy for breast cancer are rare but may include:

  • angiosarcoma of the breast
    • Angiosarcoma is a rare cancerous (malignant) tumour that starts in the lining of blood vessels or lymph vessels.
  • lung cancer
  • skin cancer

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