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Top Line: Results with partial breast irradiation (PBI) have been a bit of a mixed bag.

The Study: This probably stems from the mixed bag of techniques folks have used under the umbrella of PBI. In fact, PBI trials started as early as 1982 with poor local control—it wasn’t their fault, they were working without 3D images. Since then we’ve seen attempts at brachytherapy as well as CT-guided external beam with 3D-conformal radiation (3DCRT) using forward planning or with intensity modulated radiation (IMRT) using inverse planning. And who can forget intraoperative orthovoltage radiation? Luckily we now have a meta-analysis of all 15 randomized trials with 16,474 enrollees to clear things up. Overall, ipsilateral breast events were higher in patients treated with PBI (5%) compared to whole breast irradiation (2.8%, RR=1.72). That’s not too surprising, and what’s even less surprising is the considerable heterogeneity seen across techniques. Removing both the old-school 2D external beam and the intra-op trials, the discrepancy in ipsilateral breast events melted to 3.3% after PBI versus 2.6% after whole breast irradiation. What wasn’t heterogeneous was the consistent improvement in acute toxicity with PBI (12%) versus WBI (33%, RR=0.50). There appeared to be no significant difference in cosmesis or late toxicity after removing the outlier RAPID trial.

TBL: Robust data supports modern approaches to external beam partial breast irradiation to achieve half the rate of acute toxicity without meaningful sacrifices in local control or late cosmesis.