Modern adjuvant radiotherapy for breast adenoid cystic carcinoma: Clinical outcomes across normofractionated and hypofractionated schedules.

INTRODUCTION: Breast adenoid cystic carcinoma is a rare triple-negative breast cancer subtype with a favourable prognosis. While hypofractionated and ultra-hypofractionated radiotherapy are increasingly used for breast cancer, no dedicated data exist for breast adenoid cystic carcinoma. This study reports contemporary oncological outcomes, radiotherapy parameters, and toxicity in a uniformly treated single-institution cohort. PATIENTS AND METHODS: We retrospectively reviewed files of all patients with non-metastatic breast adenoid cystic carcinoma treated with surgery and adjuvant radiation between 2006 and 2023. Clinical, pathological, treatment, and follow-up data were analysed. Survival was estimated using Kaplan-Meier methods. RESULTS: The data from 13 women (median age 69 years, range 47-79 years) were included; 92.3 % underwent breast-conserving surgery, and all were node-negative. Hypofractionation was used in 69.2 %, including three ultra-hypofractionated regimens (32.5 Gy delivered in five fractions). At a median follow-up of 60 months, there were no regional or distant recurrences and one local recurrence salvaged surgically. Five- and 10-year cancer-specific survival rates were 100 %, overall survival rates were 90.0 % and 67.5 %, respectively, and local recurrence-free survival rate was 90.0 % at both time points. Eight patients developed grade 1 acute radiodermatitis; no other acute or late toxicity events were observed. CONCLUSION: Modern adjuvant radiotherapy for breast adenoid cystic carcinoma provides excellent long-term local control with minimal toxicity. Hypofractionated and ultra-hypofractionated schedules appear safe and efficient. Prospective collaborative studies are needed to define the role of boost and optimal fractionation strategies in this rare histology.