Accelerated partial-breast irradiation (APBI) versus whole-breast irradiation (WBI) in treatment of the biological subtypes of breast cancer: An analysis of comparative effectiveness.

45 Background: To assess if partial vs whole breast irradiation (RT) in treatment of the various biological (bio-) subtypes of breast cancer would lead to differing clinical results, a match pair analysis of APBI vs WBI was undertaken. Methods: Between 3/1993 and 9/2013 all breast CA patients (pts) treated at one institute with either APBI or WBI were matched 1:1 by follow-up (FU) +/- 15 yrs, stage and bio-subtype. This yielded 772 pts of whom 640 were luminal A, 42 luminal B, 58 triple neg (TNBC), 6 HER2+, and 26 triple +. Outcomes were analyzed across the various bio-subtypes for all the pts (APBI + WBI), APBI alone and WBI alone. The endpoints assessed were local recurrence (LR), true recurrence/marginal miss (TR/MM), elsewhere failure (EF), regional recurrence (RR), distant metastasis (DM), disease-free survival (DFS), and contralateral breast failure (CLBF). Results: Mean age was 66 (32-94) with a mean FU of 5.2 years (0.1-18.3). Regarding systemic therapy, 75% received endocrine Rx, while chemothera...