This project (Collaborative Group on Observational Studies of Breast Cancer Survivors, COBS) was set up to better understand the side-effects the may occur following radiotherapy for breast cancer.

Over 1,000,000 women who had received radiotherapy as treatment for breast cancer were included from 87 registries in 40 countries; diagnosed between 1935 and 2008 and were between 20 and 79 at the time of diagnosis.

Radiotherapy has been shown to reduce the risk of death from breast cancer for many categories of patient. However, the treatment often involves some unwanted irradiation of other tissues, particularly the heart and lungs. This can lead to an increased risk of several diseases and also of death from causes other than breast cancer. In the past, these risks have sometimes been large enough to reduce substantially the beneficial effect of the radiotherapy on survival. 

Better knowledge about the side-effects that can occur following breast cancer radiotherapy should facilitate the development of treatment guidelines, not only for breast cancer, but also for several other cancers.

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