Early Safety of Ultra-Hypofractionated Whole Breast Irradiation and Sequential Tumor Bed Boost for Early Breast Cancer (SHIFT): A Multicenter, Phase 2 Trial.

Abstract

The multicenter, single-arm, phase 2 SHIFT trial evaluated an ultra-hypofractionated radiation therapy regimen that completes both whole breast irradiation and a sequential tumor bed boost within 1.5 weeks, with the primary endpoint of acute toxicity. Patients at 4 tertiary hospitals in China aged 18 years or above with invasive breast carcinoma (pT1-3, N0-1mic, M0) or ductal carcinoma in situ after BCS were eligible. All enrolled patients underwent whole breast irradiation of 26 Gy in 5 fractions over 5 days. A sequential tumor bed boost of 10.4 Gy in 2 fractions over 2 days was at the discretion of the radiation oncologist. The primary endpoint was the incidence of grade ≥2 acute radiation-induced toxicity within 6 months after RT, including fatigue, dermatitis, and breast pain. This trial is registered at ClinicalTrials.gov (NCT04926766). Between January 2021 and July 2023, recruitment of 217 patients has been completed, of whom 209 received tumor bed boost. Within 6 months after RT, 157 (72.4%) patients experienced G1 acute toxicity only, 16 (7.4%) patients experienced G2 acute toxicity, with no G3 events observed. No toxicity event was reported in 44 (20.3%) patients. At a median follow-up of 28.3 months, no severe toxicities were found in any patient at any time during follow-up. No locoregional recurrence, distant metastasis, or death occurred. Dosimetric analysis demonstrated high protocol compliance across all centers. The integrated ultra-hypofractionated radiation therapy regimen is well-tolerated, with acute toxicity profiles confirming its favorable safety profile. Long-term follow-up is ongoing to assess late effects and efficacy.