Locoregional recurrence after breast-conserving therapy remains an independent prognostic factor even after an event free interval of 10 years in early stage breast cancer.

Introduction: Locoregional recurrence (LRR) after breast-conserving therapy is a well-known independent risk factor associated with unfavourable long-term outcome. Controversy exists concerning the prognostic impact of a LRR after a very long event-free interval.

Method: Patients who underwent breast-conserving therapy for early stage breast cancer were pooled from four European Organisation for Research and Treatment of Cancer (EORTC) Breast Group trials. Only LRR as a first event was taken into account. Risk factors such as tumour size, nodal status, young age and chemotherapy were assessed in multivariate Cox regression analysis. LRR was used as a time-dependent variable in the landmark analysis for distant disease-free survival (DFS) and overall survival (OS). Patients were categorised as having at least 0, 5 or 10 years event-free survival.

Results: In total, 7751 early stage breast cancer patients were included with a median follow-up of 10.9 years. Tumour size, nodal status, young age and chemotherapy are strong independent prognostic factors with a significant impact on long-term outcome, but lose their power and significance over time. Including all patients, LRR was the strongest prognostic factor for OS and distant DFS (resp. HR 5.01 and HR 5.31, p<0.001). In the subgroup of patients developing a LRR after at least 5 or 10 years, LRR remained the strongest independent prognostic factor for OS (resp. HR 3.98, HR 4.96, p ≤ 0.001) and distant DFS (HR 4.42, HR 7.57 p<0.001).

Conclusion: This is the first study which shows LRR after breast-conserving therapy is a very strong, time-independent prognostic factor for long term outcome in early stage breast cancer patients. These findings suggest that a LRR after a long event-free interval seems to be an indicator rather than an instigator of subsequent distant disease.