Abstract P2-11-21: A prospective phase II study of TARGeted Intraoperative radioTherapy boost plus whole breast irradiation in breast cancer patients undergoing breast-conserving treatment

Abstract

Abstract Background: TARGIT-A trial showed that intraoperative radiotherapy (IORT) using Intrabeam® concurrent with lumpectomy within a risk-adapted approach could be considered as an option for eligible patients with early breast cancer. To introduce IORT in clinical practice for Korean breast cancer patients, safety profiles for this new technique from clinical trial with Korean are required due to ethnic (anatomical) difference. Acute toxicity is a key hurdle for patients receiving IORT, because IORT may affect wound healing and increase wound complications. We conducted a phase II study as a feasibility test of IORT at the dose of 20 Gy for the replacement of boost-EBRT in Korean women who are candidates for breast-conserving treatment. Methods: This single-arm trial aimed to investigate acute toxicity occurred within 6 months after IORT. In 1,119 patients receiving EBRT from TARGIT-A trial, the incidence of acute toxicity within 6 months is 15%. Compared with WBRT, we aim to prove a non-inferiority of IORT with 20 Gy. A sample size of 195 achieves 80% power to detect a non-inferiority proportion (P0) of 0.2300 using a one-sided binomial test for non-inferiority. These results assume that the actual proportion (P1) is 0.1500. Considering a drop-out rate of 10%, the trial would need to enroll 215 patients in total. This trial is registered with ClinicalTrials.gov, number NCT02213991. Results: From August 2014 to November 2016, 233 women with early breast cancer were screened, and 215 undergoing IORT were enrolled. In 36 women, clinically significant complications during acute period are noted. The rate of patients experiencing acute toxicity was 16.7% (95% CI, 11.8-21.7%). The actual non-inferiority margin of our trial was 21.7% under the pre-specified margin as 23.0%. In details, There are 31 with seroma collection (more than 3 times when aspiration volume is over 10cc), 2 with wound infection, and 5 with skin break down. At a median follow-up of 17.8 months, there is no local recurrence. Conclusions: Targeted intraoperative radiotherapy using Intrabeam® is a safe procedure for Korean breast cancer patients with acceptable toxicity profile in acute period. Citation Format: Lee HW, Yoon C, Ahn SG, Kim JW, Cha YJ, Lee IJ, Jeong J. A prospective phase II study of TARGeted Intraoperative radioTherapy boost plus whole breast irradiation in breast cancer patients undergoing breast-conserving treatment [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-11-21.