MC1732: Pilot/Phase II Trial of Hypofractionated Radiotherapy to the Whole Breast Alone Before Breast Conserving Surgery

To report the results of our phase II trial of breast cancer patients treated with hypofractionated whole breast radiation therapy (RT) prior to breast conserving surgery (BCS).Between 2019 and 2020, patients with cT0-T2, N0, M0 breast cancer were enrolled. Patients were treated with hypofractionated whole breast RT, 25 Gy in 5 fractions, 4-8 weeks prior to BCS. RT was delivered with proton beam therapy or photons and no RT boost or regional nodal irradiation was allowed. Pathologic assessment was performed using the Residual Cancer Burden (RCB). Toxicities were assessed according to Common Terminology Criteria for Adverse Events (CTCAE, Version 4). Quality of life (QOL) was assessed with Patient-Reported Outcomes version of the CTCAE (PRO-CTCAE), The Breast Cancer Treatment Outcome Scale (BCTOS), Linear Analogue Self-Assessment (LASA), and patient-reported outcomes measurement information system (PROMIS). Deterioration of cosmesis was defined as going from excellent/good to fair/poor or from fair to poor according to the Harvard Cosmesis Scale.Twenty-two patients were enrolled. Median follow-up was 7.1 months (range, 0.2-16.8). Median age at RT was 64.1 years (range, 44.3-76.7). Tumor characteristics included: IDC 68%, ILC 14%, DCIS 5%, other 14%; grade 1 55%, grade 2 36%, 5%; ER+HER2- 95%, ER+HER2+ 5%; right-sided 68%, left-sided 32%. The DCIS were all ER+. Pre-treatment tumor size include Tis 5% and T1 95%. Median time from RT to BCS was 8 weeks. Seven (32%) patients and 3 (14%) patients experienced grade 2+ or 3 toxicity, respectively. Overall QOL LASA and PROMIS did not change significantly from baseline (P = 0.21 and P = 0.72, respectively). There was no clinically significant change (≥1 point) in any of the BCTOS domains. Patient satisfaction with treatment was high with over 90% of patients saying they would do RT again. Only 1 (5%) patient experienced a clinical deterioration that corresponded to a 'Fair' outcome on the Harvard Cosmesis Scale. At pathologic evaluation, 14 (64%) patients had RCB-0 or RCB-1 including 3 (14%) patients with a pathologic complete response (RCB-0). No local or distant recurrences have been observed.Hypofractionated whole breast RT prior to BCS yielded excellent pathologic responses. There were low rates of toxicities and good cosmesis. Further investigation into this approach with RT before BCS is warranted.