Impact of adjuvant hormonotherapy on radiation-induced breast fibrosis according to the individual radiosensitivity: results of a multicenter prospective French trial

Background: To evaluate risk of severe breast fibrosis occurrence in patients treated by breast-conserving surgery, adjuvant radiotherapy and hormonotherapy (HT) according to individual radiosensitivity (RILA assay).

Results: HT^- and RILA^high were the two independent factors associated with improved breast-fibrosis free survival (BFFS). BFFS rate at 36 months was lower in patients with RILA^low and HT⁺ than in patients with RILA^high and HT^- (75.8% and 100%, respectively; p = 0.004, hazard ratio 5.84 [95% confidence interval (CI) 1.8-19.1]). Conversely, BFFS at 36 months was comparable in patients with RILA^high and HT⁺ and in patients with RILA^low and HT^- (89.8% and 93.5%, respectively; p = 0.39, hazard ratio 1.7 [95% CI 0.51-5.65]), showing that these two parameters influenced independently the occurrence of severe breast fibrosis. BFFS rate was not affected by the HT type (tamoxifen or aromatase inhibitor) and timing (concomitant or sequential with radiotherapy).

Conclusions: HT and RILA score independently influenced BFFS rate at 36 months. Patients with RILA^high and HT^- presented an excellent BFFS at 36 months (100%).

Materials and methods: Breast Fibrosis-Free Survival (BFFS) rate was assessed relative to RILA categories and to adjuvant HT use (HT⁺ and HT^-, respectively) in a prospective multicentre study (NCT00893035) which enrolled 502 breast cancer patients (456 evaluable patients). Breast fibrosis was recorded according to CTCAE v3.0 grading scale; RILA score was defined according to two categories (<12%: RILA^low; ≥12%: RILA^high).