LAUSR

2063 Background: Treatment for oligodendroglioma in the molecular era is based on trials that used histologic criteria alone and has evolved over time to include observation and a combination of radiation (RT) and chemotherapy. In particular, treatment for high-risk patients is variable including sequential RT followed by temozolomide (TMZ) or procarbazine, lomustine, and vincristine (PCV) or chemoradiation with TMZ. This is a single institutional review of outcomes of molecular IDH mutant, 1p19q co-deleted oligodendroglioma based on initial treatment. Methods: Using both Palantir Foundry and direct record review, we stratified adult patients with grade II/III gliomas diagnosed from 1997-2017 harboring an IDH mutation and 1p/19q co-deletion based on initial treatment and excluded patients without molecular testing. Overall survival (OS) and progression free survival (PFS) were calculated by Kaplan-Meier analysis. Results: 187 patients were initially managed as: 55 (31%) observation, 16 (9%) RT alone, 51 (29%) chemotherapy alone, 39 (22%) sequential RT and chemotherapy, and 17 (10%) chemoradiation. For all patients, a subtotal (STR) or gross total resection (GTR) was associated with prolonged OS vs biopsy (NR vs 123 mos, p = 0.007). Age < 40 did not correlate with OS (p = 0.87). In the chemotherapy group, although PCV demonstrated improved PFS vs TMZ (157 vs 45 mos, p = 0.004) there was no difference in OS, only 3 patients received PCV. For patients treated sequentially with RT and PCV or TMZ vs chemoradiation, there were no differences in OS (NR vs 140 mos; p = 0.87) or PFS (49 vs 45 mos, p = 0.52), though sequential treatment trended toward prolonged survival. Conclusions: This data supports both STR and GTR as prognostic for overall survival. Despite the prolonged PFS observed with patients treated with PCV alone which did not translate to improved OS, the small PCV sample size limits the strength of this evidence. We did not find significant survival differences between sequential RT and chemotherapy vs concurrent, but interestingly, there was a trend toward improved OS in sequentially treated patients.