APBI versus ultra APBI in the elderly with low-risk breast cancer: a comparative analysis of oncological outcome and late toxicity.

AIM Accelerated partial breast irradiation (APBI) represents a validated technique for low-risk breast cancer. Recently, ultra APBI (uAPBI) using fewer than 5 fractions were described in literature. We compared clinical outcome and late toxicity after APBI or uAPBI in the elderly. MATERIAL/METHODS Two cohorts of elderly (≥ 70 years) low-risk breast cancer treated with APBI (interstitial brachytherapy) were retrospectively analyzed. A total dose of 34Gy/10f (APBI) or 16Gy/1f (uAPBI) was delivered from 2004 to 2012 and from 2013 to 2018 respectively. Oncological outcome analyzed the cumulative incidence of local relapse (LR), regional relapse (RR) and distant metastases (DM) with disease-free survival (DFS), cause-specific (CSS) and overall survival (OS). Late toxicity and cosmetic result were investigated. RESULTS A total of 157 patients (pts) (APBI: 109pts; uAPBI: 48pts) underwent APBI according to the same selection criteria. Apart from the median follow-up (97 vs. 72 months for APBI and uAPBI; p<0.002), no significant difference was noted between the two groups. Regarding 6-year oncological outcome, no significant difference was observed between APBI and uAPBI for LR (1.3% vs. 0%; p=0.4), RR (2.5 vs. 2.3%; p=0.9), DM (4.3 vs. 2.4%; p=0.6), DFS (85.2% vs. 82.2%, p=0.8), CSS (96.7 vs. 96.2%; p=0.9) and OS (86.7 vs. 82.2%; p=0.7). Regarding late toxicity, no significant difference was observed between APBI and uAPBI (total complication number: 45 vs. 33%; p=0.173) with only G1 (88.4% vs. 95%) and G2 (11.6% vs. 5%) late toxicities (p=0.677). Similarly, no significant difference was observed for excellent/good cosmetic result between the two cohorts (p=0.98). CONCLUSION We reported the first study comparing APBI vs. uAPBI in an elderly cohort with low-risk breast cancer. No significant difference was found between the two treatment groups regarding oncological outcome, late toxicity and cosmetic result. UAPBI based on a single fraction of brachytherapy represents an attractive option for therapeutic de-escalation in elderly breast cancer.