FAST NOVEMBER: A Phase II Randomized Trial of a 5 vs. 9-day Course of Whole Breast Radiotherapy With Boost for Early-stage Breast Cancer

Inclusion Criteria: * Female participant aged ≥ 18 years. --Participants must have at least one of the following risk factors: * Grade 3 invasive histology * Estrogen receptor positivity less than 5% * Lymphovascular invasion * Invasive margins \<2mm on surgical pathology * DCIS final positive margin * Extensive intraductal component * Age ≤ 50 years * Tumor size \> 2 cm * Histologically confirmed invasive carcinoma or Ductal Carcinoma In Situ (DCIS) of the breast. * Breast cancer stage (AJCC v8) T0-3, N0, M0. T0 N0 is allowed if whole breast radiation is recommended by the…