Metastasis-Directed Stereotactic Body Radiation Therapy in Oligometastatic and Oligoprogressive Solid Malignancy: Outcomes and Effect on Systemic Treatment

The purpose of this study is to present the clinical outcomes and evaluate Freedom from Introduction or Switching of Systemic Treatment (FISST) in patients with oligometastatic and or oligoprogressive disease after undergoing Stereotactic Body Radiation Therapy (SBRT). This is a retrospective review of patients with various solid tumors who received SBRT for oligometastatic or oligoprogressive cancer between the years 2019 and 2023.The primary endpoints of the study were FISST at 1 and 2-years and local control (LC) rates of the lesions that received SBRT. The secondary endpoint was overall survival (OS) at 1 and 2 years following SBRT. failure of FISST was defined as the need to introduce or switch the systemic line of treatment for any reason, or inability to provide systemic treatment when needed due to poor performance status (ECOG PS ≥ 3) or other reasons. The LC rates were estimated using the cumulative incidence method using Fine Gray's test, with death (without disease recurrence) as a competing risk. OS was analyzed using the Kaplan–Meier method and compared using log-rank test and Cox proportional hazards model. A total of 200 patients who received SBRT for metastatic sites were included. Median age was 60 (range = 22-86). The most common primary tumors were colorectal (61), breast (30), lung (28), head and neck cancers (23), prostate (16) and others (42). De novo metastasis was seen in 41.5% of the cases. A total of 257 metastatic lesions were treated. Bone was the most frequently treated site (115 lesions), be followed by liver (55 lesions), lung (44 lesions), lymph nodes (25 lesions) and adrenal glands (11 lesions). Median follow-up time was 15 months. FISST rates at 1 and 2 years were 54% and 40.36%, respectively. LC rates at 1 and 2-year were 86.30% and 79.94%, respectively. OS at 1 and 2 years were 76.5% and 64.75%, respectively. Neither the type of the primary cancer nor the histology (adenocarcinoma, squamous, mesenchymal, neuroendocrine, and others) had a significant impact on FISST ( P = 0.2953 and 0.1363) or OS ( P = 0.0892 and 0.2360). Biologically effective dose (BED) > 100 was not associated with improved FISST (HR of 1.103, 95% CI = of 0.7531 to 1.616). Although BED > 100 was associated with significantly better LC on log-rank test (HR = 0.4238, 95% CI = of 0.2078-0.8643), HR was not significant when adjusted to site of primary and histology (HR of 1.57, 95% CI = of 0.7081 to 3.527). One patient developed late grade III brachial plexopathy with no observed grade IV toxicity. SBRT is effective and safe for oligometastatic or oligoprogressive solid cancers, prolonging FISST. This suggests its potential to enhance QoL by delaying systemic treatments, especially in resource-limited settings where systemic treatment costs are prohibitive.