Background
Phase III, randomized non-inferiority trial. 4096 patients with early breast cancer (T1-3 pN0-1 M0) after BCS (85%) or mastectomy, suitable for adjuvant whole-breast or chest-wall RT. Three-arm design: conventional 40Gy/15f (START-B standard) vs two ultra-hypofractionated schedules (26Gy and 27Gy in 5 fractions over 1 week). Radiobiological modeling supports α/β ~4Gy for breast cancer, predicting biological equivalence.
Interventions and follow up
Arm A: 26Gy in 5 fractions over 1 week (ultra-hypofractionated)
Arm B: 40Gy in 15 fractions over 3 weeks (conventional START-B reference)
Primary endpoint: Ipsilateral breast tumor relapse (IBTR) at 5 years (non-inferiority)
mFollow up: 71.5 months
Arm B: 40Gy in 15 fractions over 3 weeks (conventional START-B reference)
Primary endpoint: Ipsilateral breast tumor relapse (IBTR) at 5 years (non-inferiority)
mFollow up: 71.5 months
Results
IBTR (5-yr, 26Gy vs 40Gy): 1.4% vs 1.7% — non-inferior (absolute difference -0.3%, 90% CI -1.0 to 0.4%)
IBTR (5-yr, 27Gy vs 40Gy): 2.1% vs 1.7% — non-inferior but numerically higher
Normal tissue effects (physician-assessed, 5-yr): No significant differences in breast induration, edema, or telangiectasia between 26Gy and 40Gy
IBTR (5-yr, 27Gy vs 40Gy): 2.1% vs 1.7% — non-inferior but numerically higher
Normal tissue effects (physician-assessed, 5-yr): No significant differences in breast induration, edema, or telangiectasia between 26Gy and 40Gy
Adverse events
Cosmetic/fibrosis: Moderate/marked breast induration at 5 years 7.1% (26Gy) vs 9.9% (40Gy), P=.007; breast edema and telangiectasia similar between arms; patient-reported breast appearance comparable.
Other: Pneumonitis rare in all arms; late cardiac effects not yet quantifiable at 5 years.
Other: Pneumonitis rare in all arms; late cardiac effects not yet quantifiable at 5 years.
Conclusions
26Gy in 5 fractions over 1 week was non-inferior to 40Gy in 15 fractions for IBTR at 5 years and produced comparable or slightly better normal tissue outcomes. FAST-Forward established ultra-hypofractionation as a new standard for whole-breast RT, halving treatment time from 3 weeks to 1 week.
Key Limitations
5-year follow-up may be insufficient to capture late RT effects (induration, fibrosis, rare secondary malignancies) — longer-term data are needed. Patients with regional nodal irradiation (26%) were included, but concurrent nodal RT is an active area of investigation for ultra-hypofractionation safety. The 27Gy arm, while non-inferior, showed numerically higher IBTR — 26Gy is the preferred schedule. Mastectomy patients (15%) and node-positive patients represent subgroups where ultra-hypofractionation safety data are less mature. Patient selection (BCS-dominant) and systemic therapy heterogeneity limit definitive subgroup conclusions.
Clinical Context
FAST-Forward has rapidly transformed radiotherapy practice in the UK and internationally — 26Gy/5f/1 week is now endorsed by NICE (2023) and supported by ASTRO/ESTRO guidance as an option alongside 40Gy/15f. The 1-week schedule offers major logistical, economic, and patient convenience advantages. With the COVID-19 pandemic accelerating adoption, FAST-Forward has become the preferred RT schedule in many UK and European centers. ESMO-MCBS score: N/A (RT non-inferiority trial).
References