Prognostic Factors Following Palliative Radiotherapy in Breast Cancer Patients with Oligometastatic Disease Limited to One or Two Metastatic Lesions: A Single-Center Retrospective Study

Abstract

Abstract Background: Radiotherapy plays an increasingly important role in the management of oligometastatic breast cancer (OMBC); however, prognostic factors associated with treatment outcomes remain incompletely defined. This study evaluated the clinical efficacy of radiotherapy and investigated clinical, pathological, and dosimetric factors associated with survival and local control in patients with OMBC limited one or two metastatic lesions. Methods: Nineteen patients with OMBC limited to one or two metastatic lesins treated with metastasis-directed radiotherapy between 2019 and 2025 were retrospectively analyzed. Clinical characteristics, molecular subtype, gross tumor volume (GTV), planning target volume (PTV), radiotherapy dose, fractionation schedule, and biologically effective dose (BED) were evaluated. Treatment response was assessed according to RECIST criteria. Overall survival (OS), progression-free survival (PFS), and local control (LC) were estimated using the Kaplan–Meier method. Prognostic factors were analyzed using the log-rank test and Spearman correlation analysis. Results: The median follow-up was 35 months. The objective response rate (CR+PR) was 90%, including complete response in 53% of patients, partial response in 37%, and stable disease in 5%. Median OS, PFS, and LC were 35, 18, and 24 months, respectively. Patients with smaller PTVs (<100 cc) achieved higher complete response rates (86% vs. 33%), longer PFS (46 vs. 14 months), and superior local control (36 vs. 14 months, p=0.018) compared with those with PTVs >200 cc. PTV was significantly associated with LC (p=0.007) and demonstrated a moderate inverse correlation with PFS (Spearman's ρ = −0.508, p=0.026). Higher BED (>55 Gy) was associated with improved radiological response and longer PFS; however, these differences did not reach statistical significance. Age, ER expression, PR expression, Ki-67 index, GTV, radiotherapy dose, and fractionation schedule were not significantly associated with OS, PFS, or LC in OMBC with one or two metastatic lesions . Conclusions: Palliative radiotherapy provided high local response rates and durable disease control in patients with oligometastatic breast cancer limited to one or two metastatic lesions. Smaller PTV volumes were significantly associated with longer PFS and improved local control, suggesting that irradiated tumor volume may be an important prognostic factor in this setting. Higher BED and favorable molecular subtype, particularly Luminal A disease, were also associated with more favorable outcomes. These findings support the potential role of radiotherapy in selected patients with limited metastatic breast cancer, although larger prospective studies are warranted to validate these prognostic factors