Top Line: Accelerated partial breast irradiation (APBI) is increasingly utilized in early stage breast cancer, but what are the differences in treatment modalities?
The Study: This trial emulation leveraged electronic health records across the Mayo Clinic system to compare APBI outcomes from 1026 patients with early stage breast cancer. Most of them had invasive breast cancer (87.5%) and estrogen receptor positivity (97.6%), and the median tumor size was 9mm. Photon-based RT was used in 46.9%, proton therapy was used in 30.5%, and applicator-based brachytherapy was used in 22.6%. The most common fractionation was 21.9 Gy in 3 fractions for photons and protons and 21 Gy in 3 fractions for brachy. At 5 years, the rates of ipsilateral recurrence were 3.86% for photons, 5.62% for protons, and 8.34% for brachy. After inverse probability weighting, the risk of recurrence was significantly higher with brachytherapy than with photon therapy. Proton therapy fell in between with no significant difference between it and either photon therapy or brachytherapy. These differences were most prominent among those with tumors >1cm where recurrence risk with significantly higher with brachytherapy than with photon therapy (HR 7.64).
TBL: This nonrandomized study found that applicatory brachytherapy partial breast RT had a significantly higher risk of recurrence than photon-based treatment especially among those with tumors >1cm. | Shumway, J Natl Cancer Inst 2025
The Study: This trial emulation leveraged electronic health records across the Mayo Clinic system to compare APBI outcomes from 1026 patients with early stage breast cancer. Most of them had invasive breast cancer (87.5%) and estrogen receptor positivity (97.6%), and the median tumor size was 9mm. Photon-based RT was used in 46.9%, proton therapy was used in 30.5%, and applicator-based brachytherapy was used in 22.6%. The most common fractionation was 21.9 Gy in 3 fractions for photons and protons and 21 Gy in 3 fractions for brachy. At 5 years, the rates of ipsilateral recurrence were 3.86% for photons, 5.62% for protons, and 8.34% for brachy. After inverse probability weighting, the risk of recurrence was significantly higher with brachytherapy than with photon therapy. Proton therapy fell in between with no significant difference between it and either photon therapy or brachytherapy. These differences were most prominent among those with tumors >1cm where recurrence risk with significantly higher with brachytherapy than with photon therapy (HR 7.64).
TBL: This nonrandomized study found that applicatory brachytherapy partial breast RT had a significantly higher risk of recurrence than photon-based treatment especially among those with tumors >1cm. | Shumway, J Natl Cancer Inst 2025