First Results of the Primary Outcome of a Phase II Prospective Clinical Trial to Assess the Feasibility of Preoperative Radiation Boost in Breast Cancer Patients.

A radiation (RT) boost to the tumor bed is an important component of breast-conserving therapy (BCT) in early breast cancer (BC). This prospective phase II study assessed the feasibility of delivering the RT boost pre-operatively. We hypothesize wound complication rates to be comparable to post-operative RT and the target boost volume to be smaller than standard post-operative RT. This prospective phase II trial accrued 55 patients with clinically node negative BC eligible for BCT. Patients were treated with pre-operative RT boost of 1332 cGy in 4 fractions, followed by lumpectomy and post-operative adjuvant whole breast RT to 3663 cGy in 11 fractions. The primary outcome was to demonstrate the incidence of grade 3 or more wound complications was not inferior to lumpectomy with standard postoperative whole breast RT and boost (6- 20%). We also compared the pre-op boost volume to a mock boost volume that would have been done post-operatively. Fifty-five women were enrolled between June 2021 and October 2022. Median age was 64 years-old, (range 40-77). Forty-three patients had invasive cancers and 5 had DCIS. Median clinical tumor size was 13 mm, (range 5-26). Grade 3 wound dehiscence requiring surgical revision occurred in one patient (2%). There were no other grade 3 adverse events. Three patients (6%) had grade 2 infections requiring antibiotics. The target boost volume was significantly lower that the mock post-operative volume (11cc vs. 56 cc; p <.001) Cosmetic outcome at 1st follow up was very good or excellent in 87% of patients and none had poor cosmetic outcome. The use of a pre-operative RT boost followed by whole breast RT as administered here resulted in an acceptable primary outcome with a similar rate of post-operative wound complications and smaller boost volume compared to standard postoperative RT. This approach is currently under consideration for cooperative group Phase III trial.

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