Biologic subtypes as a predictor of local control in patients with brain metastases from breast cancer after stereotactic radiosurgery

Abstract

Biological subtypes have been strongly correlated with loco-regional recurrence after definitive treatment for localized breast cancer. Brain metastases (BM) occur in 15% of patient diagnosed with breast cancer (BC). Therefore, we sought to determine whether biologic subtype is predictive of local control (LC) in BC patients with BM treated with stereotactic radiosurgery (SRS). This is a single-center retrospective study conducted with Institutional Review Board approval for the period January 1, 2004–December 31, 2018. Eligibility criteria included (1) histopathologic proven BC with documented biologic subtype, (2) presence of BM treated with SRS (single fraction), (3) follow-up MRIs, and (4) clinical follow-up. Patients were subdivided into three biologic subtypes: ER+/HER2- (“luminal”), HER2+, and ER-/PR-/HER2 (TN). All patients were treated with LINAC-based SRS with dose according to published guidelines. Cox proportional hazard model and Kaplan-Meier were used for statistical analysis of LC and overall survival (OS). With a median follow-up of 11.1 months, 17 BC BM in 50 consecutive patients were included in this study. The median disease-specific GPA was 2.0, and all patients received systemic chemotherapy and/or hormonal therapy. The 12-month LC rates for the entire cohort were 85%, 87%, and 49% for luminal, HER2+, and TN, respectively, with a significantly shorter time to local failure for the TN subtype (p = 0.014). The 12-month OS rates were 83%, 88%, and 80% for luminal, HER2+, and TN, respectively, with a trend toward shorter OS in the TN group. This study shows that in BC patients with BM treated with SRS, biologic subtype affects LC. Consideration of radiation treatment intensification or altered fractionation to improve LC may be indicated for the TN subtype. Further multicenter studies are necessary to corroborate our results.