1111 - Pre-Operative Boost Results in Low Rates of Re-Excision and Reduced Time from Initial Diagnosis to Completion of Local-Regional Treatment in Breast Cancer Patients

M. A. Chakraborty¹, Z. Sherwani², Z. Abou Yehia³, N. Ohri³, T. Cui⁴, F. Eladoumikdachi⁵, M. Kowzun⁵, S. Kumar⁵, L. Potdevin⁵, D. Toppmeyer⁶, and B. G. Haffty³; ¹Rutgers New Jersey Medical School, Newark, NJ, ²Department of Radiation Oncology, New Brunswick, NJ, ³Rutgers Cancer Institute of New Jersey, Department of Radiation Oncology, New Brunswick, NJ, ⁴Department of Radiation Oncology, Rutgers Cancer Institute of New Jersey, New Brunswick, NJ, ⁵Rutgers Cancer Institute of New Jersey, Department of Surgical Oncology, New Brunswick, NJ, ⁶Rutgers Cancer Institute of New Jersey, Department of Medical Oncology, New Brunswick, NJ

Purpose/Objective(s): Early-stage breast cancer and ductal carcinoma in situ (DCIS) are commonly treated with breast conserving surgery (BCS) followed by whole breast irradiation (WBI). Radiation tumor bed boost following BCS and WBI is also recommended depending on patient age and disease characteristics. Re-excision rates due to inadequate surgical margins are reported in the current literature to be about 17-19%. We conducted a prospective phase II clinical trial (NCT04871516) in which the boost was delivered pre-operatively instead of post-operatively. The primary endpoint is the incidence of wound complications, which was previously reported to be acceptable. Here, we report the rate of re-excision observed after pre-operative boost, which was hypothesized to be lower, and the time from initial diagnosis to end of local-regional therapy, which was hypothesized to be shorter. Materials/

Methods: Patients received a pre-operative boost of 13.32 Gy in 4 daily fractions, followed by BCS 1-3 weeks after boost, followed by WBI of 36.63 Gy in 11 daily fractions 3-8 weeks after surgery. Patient records were reviewed to assess disease and treatment characteristics. A 95% confidence interval of the re-excision rate was calculated using the Wilson-Score interval, and the Chi-Square goodness of fit test was used to compare the re-excision rate to the lower end of the currently reported range. The time from initial diagnostic biopsy to completion of radiation was retrospectively compared to 54 patients treated in a previous prospective trial using the same fractionation regimen but with sequential lumpectomy boost and to a contemporary cohort of 30 patients treated with the Canadian hypofractionation regimen using Welch’s t-test and a two-sample t-test, respectively.
Results: A total of 89 patients were included with a median age of 64 (40-79). Most, 78 (87.6%) patients, had invasive cancer while 11 (12.4%) had DCIS. The median clinical tumor size was 9 mm (1.2-33) and 9 (10.1%) patients had node positive disease. Three (3.4%, 95% CI: 1.15-9.45%) patients underwent re-excision for inadequate margins following BCS, which is lower than the literature reported rate of 17-19% (p=0.0006). The median time from initial diagnosis to completion of radiation was 109 days (42-258) in this trial, 124.5 days (62-311, p=0.00006) in the previous trial, and 132.5 days (95-220, p=0.00003) in the patients treated with the Canadian hypofractionation regimen.
Conclusion: Delivery of pre-operative boost in this prospective phase II clinical trial resulted in low rates of re-excision compared to current data for sequential boost and resulted in a reduced amount of time from initial diagnosis to completion of radiation. This may reduce treatment cost and risk of wound complications, improve treatment experience, and allow for earlier initiation of systemic therapy.