Impact of histopathological transformation and overall survival in patients with progressive anaplastic glioma

• Transformation from Grade III to Grade IV is negatively associated with survival in patients with progressive glioma.
• Radiographic features may not predict transformation of anaplastic glioma to glioblastoma.
• Molecular features of anaplastic glioma may predict likelihood of malignant degeneration.
• Tissue diagnosis at the time of progression of anaplastic glioma may direct prognosis and care.

Progression of anaplastic glioma (World Health Organization [WHO] grade III) is typically determined radiographically, and transformation to glioblastoma (GB) (WHO grade IV) is often presumed at that time. However, the frequency of actual histopathologic transformation of anaplastic glioma and the subsequent clinical impact is unclear. To determine these associations, we retrospectively reviewed all anaplastic glioma patients who underwent surgery at our center at first radiographic progression, and we examined the effects of histological diagnosis, clinical history, and molecular factors on transformation rate and survival. We identified 85 anaplastic glioma (39 astrocytoma, 24 oligodendroglioma, 22 oligoastrocytoma), of which 38.8% transformed to GB. Transformation was associated with shorter overall survival (OS) from the time of diagnosis (3.4 vs. 10.9 years, p = 0.0005) and second surgery (1.0 vs. 3.5 years, p < 0.0001). Original histologic subtype did not significantly impact the risk of transformation or OS. No other factors, including surgery, adjuvant therapy or molecular markers, significantly affected the risk of transformation. However, mutations in isocitrate dehydrogenase 1 (IDH1) was associated with longer time to progression (median 4.6 vs. 1.4 years, p = 0.008) and OS (median 10.0 vs. 4.2 years, p = 0.046). At radiographic progression, tissue diagnosis may be warranted as histologic grade may provide valuable prognostic information and affect therapeutic clinical trial selection criteria for this patient population.