A multi-institutional analysis of clinical outcomes and patterns of care of 1p/19q codeleted oligodendrogliomas treated with adjuvant or salvage radiation therapy

Purpose: Practice patterns vary for adjuvant treatment of 1p/19q-codeleted oligodendroglioma patients. This study evaluates the outcomes of adjuvant (aRT) versus salvage radiation therapy (sRT) in a multi-institutional cohort. Methods: Oligodendroglioma patients with confirmed 1p/19q codeletion who were treated with RT with or without chemotherapy from 2000 to 2017 at four tertiary centers were retrospectively reviewed. Overall survival (OS), post-RT progression-free survival (PFS), freedom-from-RT (FFRT), and radiation necrosis (RN) rates were determined using Kaplan–Meier analyses. OS1/PFS1 were defined from the initial surgery. OS2/PFS2 were defined from the RT start-date. Multivariable analyses (MVAs) of prognostic factors for OS and PFS were performed with Cox regression. Results: One hundred eighty-six patients were identified: 124(67%) received aRT and 62(33%) received sRT; of sRT patients, 58% were observed after surgery while 42% received chemotherapy without aRT. The median time from initial diagnosis to sRT was 61 months, and 74% had reoperations before sRT. sRT had longer OS1 than aRT (94% vs. 69% at 10 years, p = 0.03) and PFS1 (10-year PFS of 80% vs. 68%, p = 0.03), though sRT was not associated with significantly different OS1/PFS1 on MVAs. Chemotherapy did not delay sRT compared to observation and had worse PFS2 (42% vs. 79% at 5 years, p = 0.08). Higher RT dose was not associated with improved clinical outcomes but was associated with higher symptomatic RN rate (15% vs. 0% at 2 years, p = 0.003). Conclusions: Delaying RT for selected oligodendroglioma patients appears safe. Adjuvant chemotherapy does not delay sRT longer than observation and may be associated with worse PFS after RT.