Estimating the Risks of Breast Cancer Radiotherapy: Evidence From Modern Radiation Doses to the Lungs and Heart From Previous Randomized Trials

Authors: Taylor C., Correa C., et. al.

Source: J Clin Oncol doi: 10.1200/JCO.2016.72.0722

ascopubs.org/doi/full/10.1200/JCO.2016.72.0722

It is well-known that post-lumpectomy XRT reduces the risks of invasive and in situ breast cancer recurrence. It may also reduce the likelihood of breast cancer-related death. Women with early breast cancer are often cured of their disease. Therefore, it’s important to assess the long term health effects of breast cancer treatment. The effects of post-lumpectomy XRT on promoting lung cancer and heart disease have been contemplated for years. Since active smokers have a significantly higher risk of lung cancer compared to those who don’t smoke, it is expected that XRT in smokers would create a much higher risk of lung cancer than in nonsmokers.

The investigators reviewed the doses of post-lumpectomy radiation that were delivered to the hearts and lungs of over 40,000 women over five years. This information was combined with data about death from lung cancer among smokers and nonsmokers in the United States and the United Kingdom. Rates of death from cardiac disease were gathered from data among Western European women. The group also reviewed studies of invasive and in situ breast cancer where women did and did not receive post-lumpectomy XRT. These patients were evaluated for many factors, including disease type, recurrence and cause of death if deceased. All of this information was synthesized to predict risks of lung cancer and heart disease among smoking and nonsmoking women who received post-lumpectomy XRT.

The long term risk of lung cancer was significantly higher among smokers versus nonsmokers. That risk was most significant over 10 years after XRT was complete. The risk dropped when women stopped smoking. The risk of cardiac death was essentially equal between smokers and nonsmokers.

The group concluded that post-lumpectomy XRT in smokers may create a risk of lung cancer that is more significant than the benefits of XRT for breast cancer. Women who are being considered for that treatment should be counseled about this risk. It could be another strong argument for them to try to break the habit.