Top Line: Accelerated partial breast irradiation (APBI) has a lot of good intrinsic upsides in the name itself.
The Study: Only 5 days or less of treatment? Amazing. Less than one-third the body volume receiving radiation? Sign me up. The looming questions across all the APBI studies, then, are establishing non-inferior effectiveness and cosmesis. We know from several previous APBI trials that, when using an external beam approach on appropriately selected patients, recurrence rates are exceedingly low, as with whole breast irradiation. So that leaves cosmesis, which didn’t seem different to patients enrolled in B39 but did get worse third-party scoring in RAPID. In contrast to these trials that employed twice daily treatments for five days using 3D techniques, the phase 3 PABI-IMRT-Florence trial employed once-daily treatments for five non-consecutive days using, you guessed it, IMRT. While it achieved pretty blockbuster results at the 5-year mark in 2015, we now have the 10-year analysis. 520 women with favorable breast cancer were randomized to standard (in 2005) 50Gy/25 whole breast tangents + 10Gy/5 lumpectomy cavity boost versus 30Gy/5 every other day APBI via IMRT. The primary endpoint was “equivalence” of ipsilateral breast tumor recurrence (IBRT) defined as a <2% difference at 5 years. Per usual, events were lower than expected with rates of IBRT only 1.5% for both arms at 5 years and 2.5% versus 3.7%, respectively, at 10 years. More intriguing were the huge differences in acute/late toxicity and cosmesis in favor of APBI—you really just have to look at table 3.TBL: Unless you’re an insurance company, it’s hard to argue against the clinical superiority of 5 daily partial breast treatments with IMRT for low-risk breast cancer...at least while we await more data on breaStBRT. | Meattini, J Clin Oncol 2020