Abstract

Abstract PURPOSE/OBJECTIVE(S) Determining true recurrence versus necrosis alone after previous radiation therapy (RT) for brain metastasis based on imaging alone is difficult. Proper diagnosis is essential, as further radiation is contraindicated in the setting of radiation necrosis without tumor (TUM-). To better understand the rate of pathologic tumor positivity (TUM+) vs TUM-, we examined frozen section results from a cohort of patients with prior same-site RT undergoing resection of presumed recurrent brain metastasis (RBM). MATERIALS/METHODS Rates of intraoperative frozen section pathology disclosing tumor +/- necrosis (TUM+) or necrosis without tumor (TUM-) were examined in patients undergoing resection for presumed RBM after prior same-site RT. All cases had been prospectively enrolled on a multi-institution registry for patients undergoing resection and intraoperative cesium-131 collagen tile brachytherapy (NCT04427384)(GammaTile, GT Medical Technologies, Tempe AZ, USA). Preoperative evaluation varied by center, and patient demographics, primary site, lesion size, and prior therapies were also examined. RESULTS From 10/2020 to 2/2024 60 patients (64 lesions) underwent resection and intraoperative frozen section pathologic evaluation. Per patient, primary sites were 53% lung, 15% melanoma, 13% breast, 7% renal, and 10% other. F:M ratio was 31:29; median age 62, maximum preoperative diameter 2.9 cm, and median time from prior RT 15.4 months. Across all histologies TUM+ was seen in 88% (53/60) and TUM- in 12% (7/60). Rates of TUM- by primary type were highest for lung (16%), breast (13%), and melanoma (11%). The TUM- rate for lung metastasis was 16% vs 7% for non-lung origin. All TUM- patients received RT and prior chemotherapy, immunotherapy, or both. CONCLUSION For all previously irradiated metastasis, pathology demonstrated a 12% rate of TUM-. As all cases necessitated surgery, the adverse event grading would be ≥ Gr 4. These findings highlight the importance of pathologic confirmation before undertaking re-irradiation for presumed radiographic recurrence.