Long-term outcome after partial breast irradiation with interstitial multi-catheter high-dose-rate brachytherapy: Results from a Phase II prospective study with extended follow-up.

OBJECTIVE: To assess late toxicities, cosmesis, and oncological outcomes in patients treated with Partial Breast Irradiation (PBI) using interstitial multi-catheter high dose-rate brachytherapy. METHODS: From 2003 to 2023, 292 patients were enrolled in a prospective observational study (follow-up up to 20 years). INCLUSION CRITERIA: age ≥40 years; ECOG 0-2; ductal carcinoma in situ; invasive non lobular carcinoma; tumor size ≤2.5 cm; negative axillary lymph nodes; surgical margins ≥2 mm. PBI dose was 32 Gy in 8 fractions over 4 days. RESULTS: Invasive carcinoma accounted for 92.1% of cases. Late toxicities (mainly telangiectasia, fibrosis, liponecrosis) occurred in 100/286 patients evaluated (35%). Cosmetic outcomes were rated as excellent/good in 96% of cases. Ipsilateral breast tumor recurrence occurred in 10 patients (3.4%) with a 5-year cumulative incidence of 1.8% and 3.8% at 10 and 15 years. Breast cancer-free specific survival was 98.4% after 5 years, 95.7% after 10 years, and 94% after 15 years. Overall survival was 93% after 5 years, 69% after 10 years, and 53.4% after 15 years. CONCLUSIONS: PBI using interstitial multi-catheter high dose-rate brachytherapy is effective and well-tolerated for selected early-stage breast cancer showing excellent long-term toxicity, cosmetic profiles, and outcomes.