Abstract INTRODUCTION The Vigilant ObservatIon of GlIadeL WAfer ImplaNT (VIGILANT) registry (NCT02684838) was initiated to evaluate the use of BCNU wafers for treatment of CNS malignancies in contemporary practice and in the new era of molecular analysis. METHODS The VIGILANT registry is an observational study. Each patient receives usual care from treating physicians in routine quarterly visits, with no registry-specific visits required. The VIGILANT registry will enroll up to 500 patients at 35 US sites. Patients must be ≥18 years of age with no medical conditions increasing risk through participation. Patient follow-up will last 3 years. RESULTS The interim analysis is ongoing, with the following preliminary data. Of the 143 patients enrolled to date (mean age 59.8 ± 13.41 years, 60.1% male, 82.5% white), BCNU wafers have been implanted for newly diagnosed glioblastoma (GBM) in 49 (34.3%); for recurrent GBM in 48 (33.6%); for brain metastases in 28 (19.6%); for anaplastic oligodendroglioma in 4 (2.8%); and for other CNS tumors in 14 (9.8%). For patients with recurrent GBM, the median time from prior to current CNS tumor diagnosis was 341.5 days (IQR 88, 890). The majority of recurrent GBM patients had previously undergone systematic chemotherapy (87.5%) and radiation therapy (70.8%); only 8 (16.7%) had previously received BCNU wafers and only 4 (8.3%) had previously undergone alternating electric-field therapy. Of patients with brain metastases, 15 (51.7%) had previously undergone stereotactic radiosurgery. Of GBM patients with baseline biomarker assessments, MGMT promoter status was methylated in 52.1% (37/71), and IDH1 mutation status was positive in 15.9% (11/69). Median survival and contemporary practice patterns will be available at the time of presentation. CONCLUSIONS In the VIGILANT registry to date, BCNU wafers have been implanted most often and with equal frequency for treatment of newly diagnosed and recurrent GBM. Preliminary safety and efficacy data are pending.