Preoperative Stereotactic Body Radiotherapy for Early-Stage Luminal Breast Cancer: a Systematic Review and Meta-Analysis (PRELUMEN).

BACKGROUND AND PURPOSE:Preoperative stereotactic body radiotherapy (SBRT) has emerged as a precision locoregional strategy for early luminal breast cancer, yet no quantitative meta-analysis exists in this subtype. We aimed to estimate the pooled pathological complete response (pCR) rate, identify its predictors through meta-regression, and characterise safety and cosmetic outcomes. MATERIALS AND METHODS:A systematic review and meta-analysis of prospective trials of preoperative SBRT in patients with clinical stage T1-T2 N0-N1 luminal (ER-positive, HER2-negative) breast cancer was conducted following PRISMA 2020 guidelines. Random-effects models with REML estimation were fitted on logit-transformed proportions. Univariable meta-regression analyses examined absorbed dose (BED_4), irradiation-to-surgery interval, fractionation, technique, and biological tumor characteristics as covariates. RESULTS:Eleven prospective studies (428 patients) were included. Eight trials (N = 277) reported pCR data, yielding a pooled pCR rate of 21.4 % (95 % CI: 12.1-35.1 %; I2 = 77.0 %). The irradiation-to-surgery interval was the sole statistically significant predictor of pCR (β = +0.045 per week; p < 0.001; R2 = 98.9 %), whilst BED_4, fractionation, and technique showed no independent association. Pooled late grade ≥ 3 toxicity was 5.9 % (95 % CI: 3.7-9.1 %) and excellent or good cosmesis was achieved in 88.3 % of patients (95 % CI: 79.4-93.6 %). CONCLUSION:Preoperative SBRT achieves a clinically meaningful pCR rate in early luminal breast cancer, with acceptable toxicity and preserved cosmesis. The irradiation-to-surgery interval is the dominant modifiable predictor of pathological response. Randomized trials prospectively optimizing this interval in the luminal subtype are warranted.