The impact of adjuvant therapy for patients with high-risk diffuse WHO grade II glioma

Despite recent randomized, prospective evidence supporting use of RT and chemotherapy (CRT) for high-risk low-grade gliomas (LGG), many patients have historically received RT alone, chemotherapy alone or observation postoperatively. The purpose of this study is to evaluate outcomes for historical treatments in comparison to CRT for high-risk diffuse WHO grade II glioma patients. Records from 309 adults with WHO grade II glioma (1997–2008) eligible for RTOG 9802 (incomplete resection/biopsy or age ≥40 years) were retrospectively reviewed. Kaplan–Meier estimates were used for progression-free survival (PFS) and overall survival (OS). The Cox proportional hazards model was used for estimates of risk ratios for univariate and multivariate analyses. Median follow-up was 10.6 years. Adjuvant treatments included radiotherapy (RT) alone (45%), observation (31%), CRT (21%) and chemotherapy alone (3%). Non-astrocytic histology, TERT promoter mutation, 1p/19q codeletion and extensive resections were associated with improved PFS and OS on univariate analysis (all p < 0.05). IDH mutations and adjuvant CRT was associated with improved PFS (all p < 0.05). On multivariate analysis, histology, molecular grouping and extent of resection were significantly associated with PFS and OS. In addition, multivariate analysis revealed that CRT was associated with improved PFS and OS compared with RT alone, and improved PFS compared with observation. This study confirms the benefit of adding chemotherapy to RT compared with RT alone or observation. These findings emphasize the need for aggressive treatment in patients with high-risk LGG.