3423 - Stereotactic Body Radiotherapy (SBRT) in the Treatment of Oligometastatic Breast Cancer: A Multi-Institutional Feasibility Trial
Presenter(s)
E. Donovan1, I. Karam2, D. Vesprini3, H. Soliman4, A. Sahgal4, Y. Wang5, S. Parpia1, T. J. Whelan6, and A. Swaminath7; 1McMaster University - Juravinski Cancer Centre, Hamilton, ON, Canada, 2Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, ON, Canada, 3Sunnybrook Healthcare Institute, Toronto, ON, Canada, 4Department of Radiation Oncology, Odette Cancer Centre, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, ON, Canada, 5McMaster, Hamilton, ON, Canada, 6McMaster University, Hamilton, ON, Canada, 7Juravinski Cancer Centre, McMaster University, Hamilton, ON, Canada
Purpose/Objective(s): Patients with oligometastatic breast cancer (OMBC) may experience benefit from metastasis-directed therapy (MDT). Stereotactic body radiotherapy (SBRT) is highly ablative MDT that can be delivered with minimal toxicity. A multi-center prospective pilot study was conducted to characterize SBRT in addition to systemic therapy in patients with OMBC.
Materials/Methods: Included patients had newly diagnosed OMBC within 12 months of registration, with total metastatic disease burden limited to 5 extra-cranial sites or fewer, and received or initiated a standard systemic therapy, including chemotherapy, hormonal therapy, or targeted therapy at metastatic diagnosis. Diagnosis could be synchronous (de novo with primary disease in-situ) or metachronous (> 12 months after previous diagnosis of stage I-III breast cancer). Patients required controlled or radically treated primary disease. The primary outcome was successful accrual, planning and delivery of SBRT to all oligometastatic lesions. Patients were followed for 1 year post SBRT. Secondary outcomes including local (LR) and distant (DR) recurrence, distant progression-free survival (DPFS) and quality of life (QoL) using European Organization for Research and Treatment of Cancer Core 30 Questionnaire were evaluated. An expected 90% (confidence interval 75-97%) successful treatment rate was required, resulting in a sample size of 30 patients.
Results: 29 patients were accrued from 2018-2022 during the COVID epidemic. Median age was 52 (range 32-78). A majority of patients had estrogen (n=25, 86.2%) and progesterone receptor positive (n=19,65.5%), and Her2 Neu negative (n=24, 82.7%) breast cancers. The mean number of oligometastatic sites was 2 (range 1-5). 6 patients had synchronous and 22 patients had metachronous OMBC. 28 of 29 patients with 47 OMBC lesions successfully completed planning and delivery, or 96.6%, meeting the primary endpoint. 24 lesions received 5-fractions with median dose 30Gy (IQR 30-35Gy), while 23 lesions received two fractions with median dose 24Gy (IQR 24-28Gy). There were 26 spine, 12 non-spine bone, 4 liver, 4 nodal, and 1 lung metastasis. Median QoL scores were 5.22 (4.73 – 5.72 95% CI) at baseline, 4.8 (4.09-5.51 95% CI) on-treatment, 5.3 (4.71-5.89 95% CI) at 3 months, and 5.33 (4.72-5.94 95% CI) at 6 months.
Conclusion: SBRT is feasible to deliver in both synchronous and metachronous OMBC and appears to provide excellent local control with minimal toxicity and improvements in QoL. Further randomized studies are required to better characterize the role of SBRT in this population, particularly those with synchronous disease.
Abstract 3423 - Table 1
| Outcome | All patients (n=28) | Synchronous (n=6) | Metachronous (n=22) | |
| LR | N=3 (10.7%) | Median 352 days (range 149-390) | N= 1 (16.6%) | N= 2 (9.1%) |
| DR | N=12 (42.9%) | Median DPFS 388 days (95% CI 335 – NR) | N= 2 (33.3%) | N= 10 (45.5%) |
| PFS (events) | N=12 (42.9%) | same as above | N=2 (33.3%) | N= 10 (45.5%) |
| Alive at Study end | N=26 (92.8%) | N=5 (83.3%) | N=20 (90.1%) | |
| Toxicity (>=G3) | N=0 | N=0 | N=0 |