Abstract OT2-03-01: Multi-institution phase II trial of intraoperative electron beam radiotherapy boost at the time of breast conserving surgery with oncoplastic reconstruction in women with early-Stage breast cancer

Background: In women amenable to breast conserving therapy, lumpectomy followed by adjuvant whole breast irradiation (WBI) remains the standard of care. Randomized trials have demonstrated that the addition of a lumpectomy cavity boost significantly reduces the risk of ipsilateral breast tumor recurrences but also increases the risk of breast fibrosis. Contemporary randomized trials define the lumpectomy cavity boost volume as a 1.7 cm isometric expansion on the lumpectomy cavity as delineated on CT. However, identifying the lumpectomy cavity can be challenging, especially in women that receive adjuvant chemotherapy and in cases in which surgical clips are not present. Recently, the use of oncoplastic techniques in breast conserving surgery has increased. These techniques are used to prevent the poor cosmetic results that can occur when a large volume of breast tissue is resected. Women that undergo oncoplastic reconstruction represent especially difficult cases for lumpectomy cavity delineation. Retrospective series have evaluated the use of intraoperative electron radiotherapy (IOERT) as a boost prior to WBI in women receiving lumpectomy without oncoplastic reconstruction. In the largest series of IOERT boost prior to WBI the local control rate of this approach was >99%. Prospective data regarding IOERT boost in women undergoing oncoplastic reconstruction are limited. Advantages of this approach include direct visualization/irradiation of the tumor bed, sparing the skin of irradiation, and reducing the treatment time by ˜1 week. We hypothesize that IOERT boost followed by WBI will result in acceptably low rates of grade 3 fibrosis in women undergoing lumpectomy with oncoplastic reconstruction.

Trial Design: This is a single-arm, prospective study to evaluate the safety, toxicity and efficacy of IOERT boost at the time of breast conserving surgery in women with early-stage breast cancer undergoing oncoplastic reconstruction. Eligible women will receive 1 dose of 8 Gy to the surgical bed after lumpectomy but prior to oncoplastic reconstruction. Women will then receive adjuvant WBI of 40 Gy in 15 fractions or 50 Gy in 25 fractions.

Eligibility: Key inclusion criteria include age≥18 yo, clinically node-negative stage I/II, any breast cancer subtype.

Specific Aims: Our primary aim is to determine the rate of grade 3 breast fibrosis at 1 year. Additional aims include surgical complication rates, cosmesis, and local regional cancer control.

Statistical Methods: Safety will be evaluated by the rate of surgical complications necessitating hospital readmission or return to the operating room within 30 days of surgery+IOERT. If ≥4 events in the first 10 patients, ≥7 events in the first 20 patients, or ≥9 events in the first 30 patients are seen, the study will be halted. We hypothesize that the grade 3 fibrosis rate in our study will be ≤5%. Assuming an actual rate of 4%, an unacceptable rate of 9%, and a drop-out rate of 10%, the expected sample size is 176.

Patient Accrual: Current accrual is 0 of 176.

Contact Information: Soyhum McElroy (soyhun.mcelroy@osumc.edu) or Jose Bazan (jose.bazan2@osumc.edu)

Funding Source: Intraop Medical

Citation Format: Bazan JG, Stephens J, Terando A, Skoracki R, McElroy S, Sexton J, Gupta N, White J. Multi-institution phase II trial of intraoperative electron beam radiotherapy boost at the time of breast conserving surgery with oncoplastic reconstruction in women with early-Stage breast cancer [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 OT2-03-01.