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.