A Study of Curative-approach Treatment Along With Metastasis-Directed Stereotactic Body Radiation Therapy in...

A combination of metastasis-directed ablative therapy and curative-intent treatment for oligometastatic breast cancer is an active area of research. We designed this prospective study to explore this approach in a homogenous population of patients with oligometastatic breast cancer with bone-only metastases.

Patients with 1-5 bone-only metastases were included and received stereotactic body radiation therapy (SBRT) to the metastatic site, followed by curative-intent anthracycline and taxane-based chemotherapy and surgical excision of the primary tumor. Patients with vertebral metastases received SBRT as 30 Gy in 3 fractions over 3 days, and those with nonvertebral metastases received 24 Gy 2 two fractions over 2 days. Response assessment was done using PERCIST (PET response criteria in solid tumors). The study was designed to evaluate the progression-free survival (PFS), overall survival (OS), local control rate at the mestastatic site of SBRT, and impact of SBRT on pain control.

Between June 2021 and April 2024, a total of 49 patients with a total of 84 metastatic sites were enrolled. After a median follow-up of 19.4 months (1.1-44.4 months), median PFS was 18.8 months (1.1-44.4 months; 95% CI, 26.512-36.349), whereas the 1- and 2-year PFS were 81.63% and 71.43%, respectively. Multivariate analysis for PFS revealed that patients who completed neoadjuvant chemotherapy (P = .05) and underwent surgical excision of the primary tumor (P = .02) experienced significantly improved PFS, and hormone receptor positivity approached significance (P = .07). The median OS for the entire cohort was 19.4 months (1.56-44.4 months), whereas the 1- and 2-year OS were 89% and 74%, respectively. Multivariate analysis for OS revealed significantly improved survival for patients completing neoadjuvant chemotherapy (P = .01), receiving locoregional radiation therapy (P = .038), and presence of vertebral metastasis (P = .038). With SBRT, a high proportion of patients (96.4%) experienced a reduction in their analgesic medication requirements. The median time to achieve a pain response was 2.3 months (IQR, 1.0-4.7 months). The treatment was well-tolerated, with no documented grade 3 to 4 toxicities reported throughout the follow-up period. The most frequently observed adverse event was a temporary exacerbation of pain, known as a pain flare, which occurred in 10.7% of the patient cohort.

Oligometastatic breast cancer is a very heterogeneous group of patients. This study demonstrates excellent outcomes in treatment-naïve, bone-only metastatic patients, emphasizing the need for patient selection. This finding underscores the critical importance of careful patient stratification and selection to achieve optimal therapeutic efficacy.