First Results of the Primary Outcome of a Phase 2 Prospective Clinical Trial to Assess the Feasibility of Preoperative Radiation Boost in Patients With Breast Cancer.

Purpose: A radiation therapy (RT) boost to the tumor bed is an important component of breast-conserving therapy in early breast cancer. This prospective phase 2 study assessed the feasibility of delivering the RT boost before surgery. We hypothesize wound complication rates to be comparable with postoperative RT and the target boost volume to be smaller than standard postoperative RT.

Methods And Materials: This prospective phase 2 trial accrued 55 patients with clinically node-negative breast cancer eligible for breast-conserving therapy. Patients were treated with preoperative RT boost of 1332 cGy in 4 fractions, followed by lumpectomy and postoperative 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 preop boost volume with a mock boost volume that would have been done after surgery.

Results: Fifty-five women were enrolled between June 2021 and October 2022. Median age was 64 years old (range, 40-77 years). Forty-three patients had invasive cancers, and 5 had ductal carcinoma in situ. Median clinical tumor size was 13 mm (range, 5-26 mm). Grade 3 wound dehiscence requiring surgical revision occurred in 1 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 than mock postoperative volume (11 cc vs 56 cc; P < .001) Cosmetic outcome at the first follow-up was very good or excellent in 87% of patients, and none had poor cosmetic outcomes.

Conclusion: The use of a preoperative RT boost followed by whole breast RT as administered here resulted in an acceptable primary outcome with a similar rate of postoperative wound complications and smaller boost volume compared with standard postoperative RT. This approach is currently under consideration for cooperative group phase 3 trial.