Thursday, July 11, 20244:00 PM - 5:30 PM BP01 Presentation Time: 4:00 PM

Abstract

Purpose

To evaluate efficacy results of the GEC-ESTRO phase 3 non-inferiority trial in subgroups of patients defined by the GEC-ESTRO and ASTRO patient selection criteria for APBI.

Methods

Patients aged ≥ 40 years with low risk invasive breast cancer or ductal carcinoma in-situ after breast conserving surgery were randomized to receive either 50 Gy WBI with tumor bed boost of 10 Gy or APBI using multicatheter brachytherapy. 633/1184 patients were randomized to APBI using multicatheter brachytherapy. In the context of the current available complete results after 10 years follow-up, we report results of a supplementary sub-analysis of these latter 633 patients regarding 10-year local control rates, disease-free and overall survival results comparing subgroups categorized according to the GEC-ESTRO and ASTRO patient selection criteria for APBI. Of note, some of these criteria qualifying patients as more than low risk or as cautionary, respectively, did not occur in our patient cohort by design (c.f. in-/exclusion criteria). The trial is registered with ClinicalTrials.gov, NCT00402519.

Results

The 10-year local recurrence rate in the APBI arm was 3.5% (95% CI: 2.0-5.0%). Among 633 patients treated with multicatheter brachytherapy for APBI, according to ASTRO criteria altogether 423 patients (66.8%) were classified as “suitable”, 195 (30.8%) as “cautionary” and 11 (1.7%) as “unsuitable”; in 4 cases no ASTRO categorization was possible. In the “suitable” and “cautionary” groups, the cumulative incidence (95% CI) of local recurrence at 10 years was 3.3% and 5.0% (p=0.61), respectively; difference 1.7% (95% CI: -2.0 to 5.5%). 10-year disease-free survival was 81.9% and 83.6% (p=0.63), respectively. According to GEC-ESTRO criteria, 430 patients (68%) were classified as good candidates for APBI - “low risk group”, 203 (32%) as possible candidates for APBI - “intermediate risk group”, with no patients being in the “high risk group”. Using ESTRO criteria for subgrouping of patients, the cumulative incidence of local recurrence at 10 years was 3.5% versus 4.4% (p = 0.55) in the “low risk group” and “intermediate risk group”, respectively; difference 0.9% (95%CI: -2.6 to 4.5%). Furthermore, 10-year disease-free survival was 81.0% versus 86.4% (p = 0.11) in the “low” and “intermediate” risk group, respectively.

Conclusion

The 10-year results in patients treated with breast conserving surgery followed by APBI using multicatheter brachytherapy are comparable as well between “low risk” and “intermediate risk” groups according to GEC-ESTRO criteria as between “suitable” and “cautionary” risk groups according to ASTRO criteria. Based on the present long-term results of APBI, refinement of available recommendations for APBI patient selection criteria should be discussed to allow more patients to be treated with APBI after breast conserving surgery.