Side Effects of Radiation Therapy for Breast Cancer

Author: Courtney Misher, MPH, BS R.T.(T)
Last Reviewed: March 10, 2023

Radiation therapy is often used to treat breast cancer after surgery. The doses of radiation used to destroy cancer cells can also hurt normal cells. The damage to these normal cells is the cause of the common side effects of radiation. The side effects of radiation are directly related to the area of the body being treated. Side effects are caused by the cumulative effect (total effect over time) of radiation on the cells, which is why most patients do not have any side effects until a few weeks into their treatments. While side effects may be unpleasant, there are treatments to help deal with them. Most side effects go away slowly over time after therapy is done.

Most radiation oncologists (doctors who specialize in cancer treatment with radiation) see you once a week while you are getting treatment. This often includes a visit with other members of the care team, such as a nurse, and is a chance for you to ask questions, discuss any side effects, and find ways to help reduce side effects. However, you can report symptoms anytime to your care team.

Short-Term Side Effects

Radiation can affect each patient differently and you may not have all the possible side effects. Talk with your care team about what you can expect from your specific treatment. Some of the most common short-term side effects of radiation for breast cancer are:

  • Skin irritation: Your skin may become red, irritated, dry, or sensitive. This may start to look like a sunburn. The skin may also become darker under the arm and under the breast. In more severe cases, the skin can peel, and moist ulcers can occur. Avoid more irritation by treating your skin gently, this includes:
    • Bathing using only warm water and mild soap.
    • Avoid perfumed or scented lotions or soaps.
    • Avoid spending too much time in the sun.
  • Mild fatigue that usually gets better a month or two after treatment is done.
  • Mild tenderness in the breast or chest wall.
  • Swelling to the ipsilateral arm (the arm that's closest to the area being treated) that may make moving your arm more difficult. If you have any swelling, you should let your care team know.
  • Reduced blood counts, including neutropenia (low white cell count), anemia (low red cell count), or thrombocytopenia (low platelet count).

Short-term side effects usually happen during treatment, up until a few months after treatment.

Long-term Side Effects

Long-term effects can happen months to many years after cancer treatment. The risk of these side effects depends on the area of the breast that was included in the field of radiation and the radiation techniques that were used.

Though the risk is low, you should be aware of these possible long-term effects of radiation for breast cancer:

  • There is a low risk of developing a second cancer in or near the radiation field, called secondary cancers. They can happen from radiation exposure to the healthy tissue. Current radiation techniques are designed to limit this exposure, but it is not always possible to prevent all exposure and still achieve the desired outcomes. Yearly mammograms are important to monitor for secondary cancers.
  • Radiation to the breast, chest wall, or reconstructed breast may cause long-lasting changes to the skin, including a darkening or "tanning" of the skin. It can also cause fibrosis, a thickening or scarring of an area of tissue in the breast.
  • There can be damage to the nerves, leading to pain or loss of strength or feeling in the arm, on the side that was treated.
  • Damage to the drainage (lymphatic) system in the area can lead to chronic swelling, called lymphedema. The risk of lymphedema is higher if you also had surgical lymph node dissections (removal of lymph nodes) and, to a lesser extent, sentinel node biopsy (procedure to see if your cancer has spread). If you have lymphedema and develop pain or redness in the arm, especially with fever, you should be seen by your care team right away, as it could be a serious infection.
  • You may be at higher risk for developing cardiac (heart) problems, particularly if your cancer was in your left breast. Your radiation oncologist will develop your treatment plan to minimize the amount of radiation your heart gets. You can reduce the risk of heart problems by regularly exercising, having good dietary habits, and seeing your primary care provider for checkups.
  • Radiation pneumonitis is inflammation of the lung(s) caused by radiation that was received when treating the breast. To avoid this, the amount of radiation to the lung(s) is reduced by using different breast treatment techniques and positions. Symptoms of pneumonitis to report to your provider include shortness of breath, dry cough, chest tightness or chest pain, low-grade fever, and flu-like symptoms.
  • Radiation can cause small cracks (fractures) in the bones that are in the treatment field. If any trauma occurs (falls or accidents) notify your care team right away.

After treatment, talk with your care team about receiving a survivorship care plan, which can help you manage the transition to survivorship and learn about life after cancer. You can create your own survivorship care plan using the OncoLife Survivorship Care Plan. For more information about the long-term effects of radiation therapy for breast cancer, read our article, Survivorship: Late Effects after Radiation for Breast Cancer.


Breast cancer - types of treatment. Cancer.Net. (2021, September). Retrieved March 8, 2023, from

Radiation for Breast Cancer. Breast Cancer Treatment. (2021, October 27). Retrieved March 8, 2023, from


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