Partial Breast Re-irradiation Using Ultra Hypofractionation (PRESERVE)

Most women affected by breast cancer are treated with breast-conserving surgery to remove the tumour, followed by radiation to reduce the risk of recurrence. Unfortunately, some women will experience recurrence of the cancer in the previously treated breast. These recurrences have historically been treated by removing the whole breast or a second breast-conserving surgery followed by 3 to 5 weeks of radiation. These treatments can negatively impact mental health and quality of life or lead to harmful side effects that could impact the skin, breast, ribs, heart and lungs. Breast-conserving surgery followed by re-irradiation with partial breast irradiation (rPBI) has recently been found to be a safe alternative to mastectomy for women who have undergone prior whole breast radiation. By reducing the volume of tissue receiving radiation, rPBI has been associated with less toxicity and improved cosmetic outcomes. For many women with early-stage breast cancer, shorter 1-week (5-fraction) courses of breast radiation (ultra-fractionation) have been found to be equivalent to longer fractionation schedules in the upfront treatment setting. These 1-week schedules are more convenient for patients, with fewer treatments and shorter overall treatment time. The investigators hypothesize that a 1-week ultra-hypofractionated rPBI regimen following breast-conserving surgery (BCS) for local recurrence or new primary breast cancer in the previously irradiated breast (LR) will be associated with acceptable toxicity at 1 year (\<13% grade \>3 toxicity). The target population for this study is women with localized recurrent or new primary breast cancer in the previously irradiated breast. This is a prospective single arm phase 2 trial of external beam rPBI using 26Gy in 5 fractions delivered daily over 1-week after a second lumpectomy for LR following prior BCS and adjuvant whole or partial breast irradiation. Using a multi-institutional and international network of comprehensive cancer centers, this study will advance global knowledge of how to optimally treat women with this disease.