Radiotherapy boost dose-escalation for invasive breast cancer after breast-conserving surgery: 2093 Patients treated with a prospective margin-directed policy

Purpose: To investigate the outcome of invasive early breast cancer patients that underwent breastconserving surgery and adjuvant radiotherapy (RT), treated with a prospective margin-directed institutional policy for RT boost dose, based on final margins status (FMS). Methods and materials: A total of 2093 patients were treated between 2000 and 2008. 10 Gy boost was prescribed in case of FMS > 5 mm; 16 Gy boost with FMS between 2 and 5 mm; 20 Gy boost in case of FMS < 2 mm or positive. Results: After a median follow up of 5.2 years, we recorded 41 local relapse (LR, 2%). Concerning LR free survival, age at diagnosis, nuclear grade, hormonal status, T-stage, adjuvant hormonal therapy and adjuvant chemotherapy emerged as significant parameters (p-values from log rank test <0.05). FMS, that directed the RT boost dose, did not have significant impact on LRFS (p = 0.46). LR rates were 2.3% for FMS < 2 mm, 2.6% for 2–5 mm FMS and 1.8% for FMS > 5 mm. At multivariate analysis, higher nuclear grade (p = 0.045), triple negative subtype (p = 0.036) and higher T-stage (p = 0.02) resulted as the independent predictors of LR occurrence. Conclusions: Our experience showed that a margin-directed policy of RT boost dose-escalation seems to reduce the negative impact of FMS on LR, but it is not able to overcome the unfavorable effect of higher nuclear grade, higher T stage and triple negative subtype.