Continuing risk of ipsilateral breast relapse after breast-conserving therapy at long-term follow-up

Currently, the local treatment of most patients with early invasive breast cancer consists of breast-conserving therapy (BCT). We have previously reported on the risk factors for ipsilateral breast relapse (IBR) in 1,026 patients treated with BCT after a median follow-up of 5.5 years. In the present study, we evaluated the IBR incidence and the risk factors for IBR after prolonged follow-up.

We updated the disease outcome for all 1,026 patients using the clinical information collected from the medical registration of The Netherlands Cancer Institute and performed step-wise proportional hazard Cox regression analysis to identify the risk factors associated with an increased risk of IBR after BCT at long-term follow-up.

After a median follow-up of 13.3 years, 114 patients had developed an IBR as the first event. The IBR rate was 9.3% and 13.8%, respectively, at 10 and 15 years. Also, the increase in IBR was continuous without reaching a plateau, even after 15 years. Univariate analysis showed that involved surgical resection margins, young age, vascular invasion, and the presence and quantity of an in situ component are risk factors for IBR. Multivariate analysis showed that tumor-positive surgical resection margins (hazard ratio, 2.9; 95% confidence interval, 1.7-5.2, p = 0.0002) or the presence of vascular invasion (hazard ratio, 2.0; 95% confidence interval, 1.2-3.2, p = 0.004) is the major independent risk factor for IBR.

The data from long-term follow-up showed a constant increase in IBR among patients treated by BCT, even after 15 years, without reaching a plateau. Involved surgical resection margins and vascular invasion were the most important risk factors for IBR.