NCOG-10. RADIATION THERAPY CAN BE SAFELY DEFERRED IN OLIGODENDROGLIOMAS

Abstract

Abstract Deferring multimodal aggressive therapies in young patients to delay treatment-induced toxicity without jeopardizing long-term outcome would be of great benefit to our patients. After IRB approval, we retrospectively reviewed 80 confirmed IDH mutant and 1p19q codeleted oligodendrogliomas treated at one institution between 2005 and 2020. Median follow-up was 5 (range 1-26) years. All patients underwent maximal safe resection, followed by observation with routine imaging (n=28), chemotherapy alone (n=27), or radiation with chemotherapy (n=25) as initial upfront therapy. Median progression free survival was 36 (range 1-203), 54 (range 1-306), and 57 (range 4-281) months, respectively. Median overall survival was not reached, with 85% (67/80) alive, 8 on treatment and 59 stable off therapy. Among 35 patients who died or were followed for 10 years, median PFS was 12, 15, and 10 years for observation (n=9), chemotherapy (n=11) and chemoradiotherapy (n=15), with deaths or KPS below 50 in 3, 6, and 8, respectively. Three deaths in the observation group occurred 12, 12 and 17 years after diagnosis; one at 95 years old and another tumor-unrelated. Among 44 patients eventually receiving radiation, 15 suffered toxicity, including pathologically proven necrosis (n=6), cognitive decline with KPS< 50 (n=5), memory loss with KPS > 50 (n=3), and optic neuropathy (n=1). Myelosuppression from PCV was more pronounced after chemoradiation than in the upfront setting. Temozolomide after PCV chemotherapy was well tolerated. Long term follow-up of oligodendroglioma patients is challenging, but essential in determining late toxicities and treatment efficacy. Long-term results of European and North American multicenter cooperative group trials contradicted earlier publications reporting no benefit from early chemotherapy. Some management practice guidelines established a half-century ago persist (i.e., administer radiation therapy early), despite potentially crippling late effects. Deferring upfront radiation therapy is safe, less toxic, and equally efficacious in codeleted oligodendrogliomas.