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MO_16_2895 - Spine Stereotactic Body Radiation Therapy with Concurrent Systemic Therapies for Treatment of Metastatic Breast Cancer

Monday, October 22
10:45 AM - 12:15 PM
Location: Innovation Hub, Exhibit Hall 3

Spine Stereotactic Body Radiation Therapy with Concurrent Systemic Therapies for Treatment of Metastatic Breast Cancer
R. H. Zhuang1, M. Y. Lee2, E. H. Balagamwala3, L. Angelov4, J. H. Suh5, and S. T. Chao5; 1Case Western Reserve University School of Medicine, Cleveland, OH, 2Cleveland Clinic Lerner College of Medicine, Cleveland, OH, 3Department of Radiation Oncology, Taussig Cancer Institute, Cleveland Clinic, Cleveland, OH, 4Department of Neurosurgery, Cleveland Clinic, Cleveland, OH, 5Department of Radiation Oncology, Taussig Cancer Center, Cleveland Clinic, Cleveland, OH

Purpose/Objective(s): With the increasing prevalence of targeted breast cancer therapies, there is a greater need for understanding the toxicity profile with sSBRT and concurrent systemic agents. Our study investigates whether concurrent systemic therapies are associated with increased risk for pain flare and vertebral compression fracture.

Materials/Methods: We conducted a retrospective review of metastatic breast cancer patients who underwent sSBRT at a single tertiary care institution. sSBRT-associated toxicities, including pain flare and pathologic compression fracture at 12 months, were recorded. Multivariate competing risks regression was used to model associations between toxicity-related outcomes and dosimetric, clinicopathologic, and demographic factors.

Results: 65 patients (103 treatments) met inclusion criteria, 66.3% of which were luminal A, 16.8% luminal B, and 10.9% HER2+. 68 treatments (66%) received concurrent therapies, which included cytotoxic therapy (10.7%), EGFR TKIs (2.9%), HER2 antibody (17.5%), and hormone therapy (48.5%). Median KPS was 80 (range, 60-100); median prescription dose was 16 Gy (range, 12-18 Gy) in 1 fraction, with a median follow up time of 14.3 months. HER2-amplification (HR 0.43, p=0.03), prior surgery (HR 0.57, p<0.01), and uncontrolled systemic disease status (HR 0.73, p=0.03) were associated with decreased risk for pain flare, whereas concurrent HER2 antibody was associated with increased risk for the development of pain flare (HR 2.59, p=0.03). Oligometastatic disease (HR 1.45, p=0.05), concurrent HER2 antibody (HR 2.12, p=0.05) and concurrent hormone therapy (HR 1.94, p=0.04) were associated with increased risk for the development of vertebral compression fracture.

Conclusion: Concurrent HER2 antibody and hormone therapy have demonstrated an increase in sSBRT-associated toxicities, specifically pain flare and vertebral compression fracture. Although the risk for pain flare and vertebral compression fracture is increased, it does not preclude the use of sSBRT in patients with breast cancer undergoing HER2-directed and hormonal treatments, since both of these toxicities can be managed with conservative measures. Further study is warranted in this group to establish the role of concurrent agents with spine SBRT.

Author Disclosure: R.H. Zhuang: None. M.Y. Lee: None. E.H. Balagamwala: Employee; Cleveland Clinic. J.H. Suh: Consultant; ACMUI. Board member; Korean American Society for Therapeutic Radiation. S.T. Chao: Honoraria; Varian Medical Systems, Zeiss, Abbvie. Consultant; Abbvie.

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