Introduction: Although surgery plays a crucial diagnostic role in 1p/19q-codeleted, World Health Organization (WHO) grade 2 diffuse oligodendrogliomas, the role of maximal tumor surgical resection remains unresolved, with early retrospective series limited by the rarity of these tumors, lack of molecular classification, and substandard assessments of extent of resection.[1,2]

Methods: The characteristics, management, and overall survival (OS) of patients >20y.o. who presented with biopsy-proven 1p/19q-codeleted WHO grade 2 diffuse oligodendrogliomas during 2010-2015 were evaluated using the National Cancer Database, which comprises 70% of all newly diagnosed U.S. cancers. Patients were stratified based on whether they underwent surgical resection within 3-months of diagnosis or managed with watchful-waiting (biopsy-only cohort). Patients receiving chemotherapy or radiotherapy were excluded to prevent confounding. Dichotomous variables were compared by multivariable logistic regression. OS was estimated by Kaplan-Meier methods and compared by log-rank test and risk-adjusted proportional hazards.

Results: There were 473 patients with biopsy-proven 1p/19q-codeleted WHO grade 2 diffuse oligodendrogliomas who did not receive adjuvant therapy, of which 84.6% (n=400) underwent surgical resection. Of patient and tumor characteristics, only younger patients were more likely to be resected – resection was independent of patient sex, comorbidities, race/ethnicity, insurance status, tumor location, or tumor size (all p<0.05). Of those that were resected, 46.0% (n=261) had gross total resection (GTR), which was significantly associated with private insurance (OR 2.8, 95CI: 1.1-7.2, p=0.03) and independent of other patient or tumor characteristics. In risk-adjusted analyses, GTR, but not subtotal resection (STR), demonstrated improved OS (vs. biopsy only: HR 0.1, 95CI: 0.0-0.7, p=0.02). Unadjusted 5-yr OS rates were biopsy-only: 94.0% (95CI: 82.1-98.1), STR: 92.7% (95CI: 82.2-97.1), and GTR: 97.1% (95CI: 93.0-98.9).

Conclusions: WHO grade 2 1p/19q-codeleted diffuse oligodendrogliomas that are amenable to resection demonstrate improved OS with GTR in a national cohort, as compared to biopsy-only watchful waiting.

Patient Care: The role of maximal tumor surgical resection in 1p/19q-codeleted, World Health Organization (WHO) grade 2 diffuse oligodendrogliomas remains unresolved, with early retrospective series limited by the rarity of these tumors and substandard assessments of extent of resection. Using an extensive national cohort and current revised 4th ed WHO classification schema, we demonstrate the overall survival benefits associated with maximal resection in these patients.

Learning Objectives: 1) What are the patient and tumor characteristics predictors of management by watchful waiting vs. surgical resection in 1p/19q-codeleted WHO grade 2 diffuse oligodendrogliomas? 2) What are the patient and tumor characteristics associated with extent of resection in 1p/19q-codeleted WHO grade 2 diffuse oligodendrogliomas? 3) What are the overall survival benefits associated with extent of resection in 1p/19q-codeleted WHO grade 2 diffuse oligodendrogliomas?

References: 1. Central Nervous System Cancers (Version 1.2017). National Comprehensive Cancer Network. https://www.nccn.org/professionals/physician_gls/pdf/cns.pdf. 2. van den Bent MJ, Smits M, Kros JM, Chang SM. Diffuse Infiltrating Oligodendroglioma and Astrocytoma. J Clin Oncol. 2017;35(21):2394-2401. doi:10.1200/JCO.2017.72.6737