MLTI-05. Adjuvant re-irradiation improves local control of surgically resected recurrent brain metastases

BACKGROUND: The efficacy of salvage resection (SR) of recurrent brain metastases (BrM) post-stereotactic radiosurgery (SRS) is not well described. We sought to characterize the impact of adjuvant post-salvage radiation therapy (PSRT) in this setting and identify tumor-specific variables that influence local control. METHODS: Retrospective analysis of post-SRS recurrent BrM that underwent SR between 2003–2020 at Memorial Sloan Kettering Cancer Center was performed. Cases with histologically-viable malignancy were included and stratified by receipt of adjuvant PSRT within 60 days of SR (PSRT cohort) vs. observation (observation cohort). Resection-site outcomes were described using cumulative incidences and univariate and multivariate competing risks regression accounting for clustering. RESULTS: One-hundred fifty-five recurrent BrM in 135 patients were included. Thirty-nine (25.2%) of the post-operative cavities were treated with adjuvant PSRT, and the remaining 116 (74.8%) cavities were initially observed. Gross- or near-total resection was associated with significantly improved local control compared to subtotal resection (p=0.007). Adjuvant PSRT was associated with a reduced rate of LR at 6 months [18.0% (95%CI: 9.8–33.1%) vs. 35.9% (95%CI: 27.9–46.2%) with initial observation] and 12 months [28.8% (95%CI: 17.0–48.8%) vs. 43.9% (95%CI: 36.2–53.4%)]. On multivariate analysis, adjuvant PSRT (p=0.095), low tumor-viability within the resected BrM (p=0.17), and first-time resection (p=0.035) all independently trended towards improved local control. BrM size at SR (≥3cm vs. <3cm, p=0.48), primary malignancy (p=0.35), and specific PSRT modality (whole or partial brain radiation vs. SRS, p=0.43) were not associated with differences in LR rate. Radiation necrosis (RN) was significantly increased in the PSRT cohort (HR 4.55, 95%CI: 1.26–16.39, p=0.02), though the total percentage with symptomatic RN remained low (PSRT cohort 5.1% vs observation cohort 0.9%). CONCLUSIONS: Local control after SR of a recurrent BrM may be optimized with gross- or near-total resection and adjuvant post-operative re-irradiation, with low symptomatic RN.