Abstract P2-11-22: Adjuvant radiation is associated with decreased risk of locoregional recurrence in patients with micrometastatic invasive breast cancer
Authors: Burr AR , Brickson CR , Anderson BM 
Published: February 2018

Purpose: Determining the appropriate adjuvant treatment in patients with micrometastatic disease remains a considerable challenge in the treatment of breast cancer. Recent data suggests patients with micrometastatic disease have an intermediate risk of locoregional recurrence between patients with macrometastatic disease and patients with no evidence of axillary disease. Further work is needed to tailor treatment strategies to individual patients based on tumor characteristics. Here, we reviewed the outcomes of patients with N1mic axillary disease treated at the University of Wisconsin to assess the risk of locoregional recurrence in patients with micrometastases to determine risk factors associated with increased risk of LRR.

Methods: We identified patients with pathologic T1-T3, N1mic invasive breast cancers treated at the University of Wisconsin between 01/01/2004 and 07/01/2015. The patients were identified within the UW breast cancer registry and by query of pathologic records. We utilized the Kaplan-Meier method to determine the rate of locoregional recurrence free survival and overall survival. Multivariate analysis of patient and tumor characteristics was performed using the Cox proportional hazards model using locoregional recurrence as an outcome.

Results: 154 patients were identified with micrometastatic disease with a median follow-up of 4.1 years. The 5 year locoregional recurrence free survival and overall survival for all patients was 92.6% and 88.9%, respectively. On univariate analysisl, ER negative status (HR 8.03, p&lt;0.001), PR negative status (HR 3.18, p =0.49), Her2 amplification (HR 5.02, p=0.005), and tumor grade (HR 2.96, p=0.005) were all significantly associated with increased risk of locoregional recurrence (LRR). Radiation therapy (HR 0.174, p=0.005) was the only therapeutic variable associated with decreased risk of LRR. Lymphovascular space invasion, close or positive margins, extranodal extension, and tumor stage were not associated with risk of LRR. Additionally, the type of axillary surgery, the type of breast surgery, the use of chemotherapy, and the use of endocrine therapy were not associated with risk of LRR. On multivariate analysis, ER negative status (HR 6.39, p=0.004), Her2 amplification (HR 5.53, p=0.006), and treatment with radiation (HR 0.14, p=0.004) remained significantly associated with risk of LRR.

Conclusion: The data presented suggest that treatment with radiation is associated with decreased LRR in patients with micrometastatic disease. Patients with Her2 amplification or ER negative status are also found to be at particularly high risk of recurrence. Future work is needed to determine strategies to decrease the rates of recurrence in these high risk groups and to define subgroups of patients with micrometastatic disease for whom radiation is particularly beneficial.

Citation Format: Burr AR, Brickson CR, Anderson BM. Adjuvant radiation is associated with decreased risk of locoregional recurrence in patients with micrometastatic invasive breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-11-22.