[Purpose] The Groupe European de Curietherapie-European Society for Therapeutic Radiology and Oncology (GEC-ESTRO) has reported the equivalent outcomes of partial-breast irradiation (PBI) using multicatheter interstitial brachytherapy (MCB) to whole-breast irradiation (WBI) in breast-conserving therapy, showing that the incidence of local recurrence was 1.44% with MCB-PBI and 0.92% with WBI. Based on the trial, MCB-PBI could be considered as an alternative method to WBI for low-risk breast cancer patients. However, it would be difficult to translate it directly into Japanese community practice. After categorization of Japanese patients using the inclusion and exclusion criteria of this trial, our databases were re-evaluated to validate the data for Japanese patients, and the possibility to extend the candidate for MCB-PBI was also investigated.

[Methods] Patients undergoing BCT were retrospectively examined between November 2007 and December 2015. The technique involved an open-cavity implant with a dose of 32 Gy in eight fractions. WBI was performed with a total dose of 50 Gy in fractions of 2 Gy. The 4-year clinical outcomes of MCB-PBI were evaluated in the two distinct categories, and comparisons of outcomes between MCB-PBI and WBI were performed in patients with unfavorable features.

[Results] Of a total of 501 lesions undergoing BCT, 301 lesions were treated with MCB-PBI and 200 lesions with WBI. At a median follow-up time of 52 months, the 4-year rate of ipsilateral breast tumor recurrence (IBTR)-free, disease-free, and overall survival in patients with MCB-PBI and WBI were 98.9% vs. 98.0% (p = 0.56), 97.0% vs. 95.3% (p = 0.78), and 99.6% vs. 98.2% (p = 0.38), respectively. In the exclusion cohort treated with MCB-PBI, IBTR-free and disease-free survival were significantly poorer than in the inclusion cohort.However, no significant differences in the outcomes between the two radiotherapy techniques were demonstrated with respect to either IBTR-FS (95.0% vs. 97.2%, p = 0.24), DFS (95.0% vs. 95.8%, p = 0.31), or OS (100% vs. 99.0%, p = 0.80) in patients with exclusion criteria

Univariate and multivariate analysis of prognostic factors for IBTR and breast cancer event

Variables IBTR     Locoregional and distant recurrences     
  P-value     P-value     
  Univariate Multivariate HR (95% CI) Univariate Multivariate HR (95% CI) 
Age ≥ 40 vs < 40years .25 — 2.49 (0.53–11.72)   — 0.90 (0.21–3.85) 
Axillary node negative vs. positive <.05 <.05 4.09 (1.18–14.12) <.05 <.05 2.75 (1.19–6.36) 
Margin negative vs. positive <.01 <.01 5.58 (1.54–20.29) .075 .068 2.55 (0.93–6.97) 
WBI vs. MCB-PBI .56 — 0.69 (0.20–2.39) .78 — 0.89 (0.39–2.03) 
Variables IBTR     Locoregional and distant recurrences     
  P-value     P-value     
  Univariate Multivariate HR (95% CI) Univariate Multivariate HR (95% CI) 
Age ≥ 40 vs < 40years .25 — 2.49 (0.53–11.72)   — 0.90 (0.21–3.85) 
Axillary node negative vs. positive <.05 <.05 4.09 (1.18–14.12) <.05 <.05 2.75 (1.19–6.36) 
Margin negative vs. positive <.01 <.01 5.58 (1.54–20.29) .075 .068 2.55 (0.93–6.97) 
WBI vs. MCB-PBI .56 — 0.69 (0.20–2.39) .78 — 0.89 (0.39–2.03) 
.

ConclusionsTo our knowledge, this study includes the largest cohort of Asian patients undergoing MCB-PBI. Although the retrospective chart review with relatively short follow-up time and small number of patients does not allow reaching any definite conclusion, we could expect the same outcomes by MCB-PBI as those in the GEC-ESTRO trial with respect to the tumor control only for Japanese but for Asian patients with breast cancer. Moreover, no negative impact on the outcomes of MCB-PBI as compared to WBI was not found in patients with exclusion criteria.

Citation Format: Sato K, Mizuno Y, Fuchikami H, Takeda N, Kato M. Re-evaluating outcomes of partial-breast irradiation using multicatheter brachytherapy for Japanese patients with breast cancer by European brachytherapy phase 3 trial [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P1-11-12.