Ipsilateral breast tumour recurrence (IBTR) dynamics in breast conserving treatments with or without radiotherapy

Purpose:To study whether ipsilateral breast tumour recurrence (IBTR) dynamics are modified by post-operative radiotherapy (RT). Methods and materials:The hazard rate for IBTR was analysed in a database from patients undergoing breast conserving surgery with or without post-operative radiotherapy within randomised clinical trials from the Milan Cancer Institute. Results:The hazard rate for IBTR presents a bimodal pattern. Post-operative radiotherapy, in addition to reducing IBTR incidence from 24.5 to 5.8 at 10 years, causes more than a one year delay in its clinical manifestation. Distant metastasis dynamics are not modified by radiotherapy administration. Conclusions:In the light of a biology-based model of breast cancer metastasis development, IBTR peak delay most likely originates in a more prolonged dormancy time that, in turn, is related to local microenvironment conditions. Present clinical findings suggest that, besides a direct killing effect on residual tumour cells, microenvironmental modifications may play a major role in RT effectiveness.