Impact of Stereotactic Body Radiotherapy (SBRT) in Oligoprogressive Metastatic Disease

Purpose/Objective(s) There is increasing interest in using stereotactic body radiation therapy (SBRT) to areas of oligoprogressive metastatic disease (OPD) to allow for the prolongation of a patient's current systemic therapy regimen or delay the need to start a new regimen. The main objective of our study was to investigate the impact of SBRT on survival and the incidence of systemic therapy treatment switch in this group of patients. Materials/Methods A retrospective institutional review of patients treated with SBRT for OPD was performed. Patients were included if they received SBRT for 1-3 discrete progressing metastases, using a dose of at least 5 Gy per fraction. The study aimed to calculate progression free survival (PFS), overall survival (OS), local control (LC) and incidence of treatment switch (TS). PFS and OS were calculated using Kaplan-Meier methodology, while LC and TS were determined using cumulative incidence to account for competing risks of death without progression. Results Eighty-one patients with a total of 118 lesions were treated with SBRT from July 2014-November 2020. Median SBRT dose was 40 (18-60) Gy in 5 (2-8) fractions. Patients with kidney, lung, and breast cancer constituted the majority of patients. The last systemic therapy prior to OPD was tyrosine kinase inhibitor (TKI) (30.9%), chemotherapy (29.6%), immunotherapy (12.3%), chemo/VEGF (8.6%), hormonal (6.2%), CDK 4/6 (2.5%). Ten percent were on surveillance for indolent metastatic disease. Median follow-up post SBRT was 14 months. Median OS and PFS were 25.1 (95% CI 11.2 – 39.1) months and 7.8 (95% CI 4.6-10.9) months, respectively. The cumulative incidence of local progression of treated lesions was 5% at 1 year and 7.3% at 2 years. Sixty patients progressed after SBRT (mostly distant failure) and 17 underwent additional SBRT for further OPD. Thirty-eight patients (47%) ultimately changed systemic therapy following SBRT; the cumulative incidence of TS was 28.5% at 6 months, 37.4% at 1 year, and 43.9% at 2 years. Overall, after SBRT there were 16 acute and 2 late, grade 3 toxicities and no grade 4 or 5 acute or late toxicity observed. Conclusion SBRT effectively controls locally progressing lesions but distant progression still occurs frequently. However, a sizeable number of patients can be salvaged by further SBRT or have minimally progressing disease that may not warrant an immediate initiation or switch in systemic therapy. This is illustrated by the fact that over half the patients did not require a TS at two years. Further prospective studies are warranted to validate the benefit of integrating SBRT with systemic therapy strategies for patients with OPD.