Clinical equipoise exists around the optimal time to start adjuvant endocrine therapy in patients who will receive post-operative radiotherapy for breast cancer. Patients receive either concurrent or sequential endocrine and radiation therapy, where concurrent therapy consists of endocrine therapy started before, with or during radiotherapy, while sequential treatment is defined as endocrine therapy starting after the completion of radiotherapy. A recent survey of Canadian oncologists showed that the main reason for prescribing sequential endocrine therapy was a concern that concurrent endocrine therapy and radiotherapy would worsen the toxicity of endocrine treatment. This is despite the absence of any clinical trial evidence to support this. Indeed, a recent systematic review by our group was unable to confirm or refute whether increased toxicities, related to the timing of endocrine therapy and radiotherapy actually exist in clinical practice. The investigators are therefore proposing a pragmatic randomised trial to assess whether or not concurrent endocrine therapy and radiotherapy worsens endocrine treatment-related symptoms in an era of modern endocrine and radiation therapy.
