Preliminary Report of Partial-breast Irradiation Following Neoadjuvant Chemotherapy from COMBAT-NEO: Clinical Outcome of Multicatheter BrAchyTherapy after NEOadjuvant Chemotherapy

Background: Breast-conserving therapy (BCT) with partial-breast irradiation (PBI) has become a standard alternative to whole-breast irradiation. Recently, neoadjuvant chemotherapy (NACT) has been widely performed for early breast cancer. Although BCT using perioperative PBI decreased invasiveness and geographic miss, risks of adverse events and local recurrence remain a concern for patients receiving NACT. Thus, a prospectively registered study, the Clinical Outcome of Multicatheter BrAchyTherapy after NEOadjuvant chemotherapy (COMBAT-NEO), was conducted. Methods: Patients who underwent BCT using multicatheter-interstitial brachytherapy (MIB) by intraoperative catheter implant were analyzed. Early and late adverse events (AEs) including higher grade skin toxicities and wound complications, and tumor control of patients receiving NACT were evaluated in comparison with adjuvant chemotherapy (ACT) and no chemotherapy (no-CT). Results: Between April 2017 and February 2020, 265 consecutive patients who received single-stage BCT were evaluated, including 13 NACT (4.9%), 68 ACT (25.7%), and 184 no-CT (69.4%). The median follow-up time and age were 30.0 months and 59.0 years, respectively. All patients were followed up for at least 12 months. Although AEs in NACT, ACT, and no-CT were observed in 1 (7.7%), 5 (7.4%), and 11 (6.0%) patients, respectively (p = 0.91) and there was no acute AE in NACT patients. Overall, 3 (1.1%) ipsilateral and 1 (0.4%) contralateral breast tumor recurrences were observed in no-CT patients. There were no regional and distant recurrences. Conclusion: Although this pilot study was based on a small sample size with short follow-up, these preliminary results support the study of a single-stage BCT with MIB-PBI following NACT