Grant: Operating Grant

Local breast radiotherapy (RT) is standard therapy for all women with lymph node negative (LNN) early stage breast cancer. We have always wondered whether we might be over-treating some of these patients, whose outcomes are so good, even without breast RT. We have previously attempted to ask this question, in the form of a randomized clinical trial, whereby half of the patients did NOT receive breast RT, but were treated only with hormones such as Tamoxifen. Disappointingly, breast RT was still required, in that without RT, >8% of women will experience breast recurrence, which was unacceptably high. There have been extensive molecular studies conducted on breast cancer, resulting in the identification of different subtypes such as luminal A, luminal B, HER2-enriched, etc. Many of these molecular platforms are very expensive, so that we have been developing less expensive methods, such as immunohistochemistry, to distinguish the various breast cancer subtypes. Last year, we successfully determined that women with luminal A breast cancer are the most favourable subgroup, with the highest probability of surviving without local breast recurrence (92%). Extending this work, using tumours from participants in our randomized trial, we have generated preliminary data which not only corroborated that luminal A patients had the lowest risk of local relapse (~5%), but furthermore, RT had no additional benefit. The current project proposes to complete the evaluation of using six immunomarkers on at least 592 samples, to corroborate our initial observations. If correct, we will proceed to a future clinical study, where all luminal A LNN breast cancer patients, over the age of 60, will be treated with hormones only, thereby spared from RT, resulting in significant benefit to both patients, and the Canadian health care system.