P03.02.B VIABLE TUMOR RECURRENCE IS A MAJOR CAUSE OF LOCAL FAILURE AFTER BEVACIZUMAB THERAPY FOR RADIATION NECROSIS IN BRAIN METASTASES TREATED WITH STEREOTACTIC RADIOSURGERY

Abstract

Abstract BACKGROUND Bevacizumab (BVZ) is known to be effective to control radiation necrosis (RN) following stereotactic radiosurgery (SRS) for brain metastases (BMs), although treatment failure may occur. Here, we investigated the incidence and pattern of local failure after BVZ therapy for RN and its underlying biological mechanism. MATERIAL AND METHODS We conducted a retrospective analysis on 17 patients who had been treated with BVZ for RN following SRS for BMs between 2016 and 2021. In each patient, the diagnosis of RN was made based on the conventional and advanced MR with or without positron emission tomography. Median 5 cycles (range, 2-10 cycles) of BVZ (5 mg/kg) were administered at 2-week intervals. Treatment response was assessed by volumetric changes of the lesions on MR and patients’ neurological status. RESULTS Treatment response was typically brisk and substantial. Best MR response was seen at median 13 weeks (range, 3-56 weeks) after the start of BVZ with a median volume decrease of 84.5% (range, 38.7-100%) of perilesional brain edema on T2WI and of 54% (range, 2.9-100%) of contrast enhancing lesions on T1WI. Patients’ neurological status improved in 16 patients (94.1%) and was stationary in 1 (5.9%). During the median follow-up of 12 months (range, 2-60 months), delayed local failure was observed in 6 patients (35.3%) at median 10 months (range, 6-14 months) after starting BVZ treatment, where viable tumor recurrence was demonstrated in all of them. No reconstitution of RN without viable tumor was observed during the follow-up. CONCLUSION Although BVZ was highly effective to control RN following SRS for BMs, delayed local failure frequently occurs owing to viable tumor recurrence. This may imply that much predominant vascular stabilizing effect of BVZ over anti-tumor effect transiently obscures the presence of potential viable tumor cells but does not prevent them from eventual recurrence.