MPC-4 Malignant transformation of diffuse low-grade gliomas: systematic review and meta-analysis

While malignant transformation of diffuse low-grade glioma (LGG) is a critical event affecting the patient survival, the incidence and related factors have been inconsistent in the literature. According to the PRISMA guideline, we systematically reviewed articles from 2009, meta-analyzed the incidence of malignant transformation and clarified factors related to the transformation. Forty-one articles were included in this study (n = 7122). We identified two definitions of malignant transformation: histologically proven (Htrans) and clinically defined (Ctrans). The malignant transformation rate curves in Htrans and Ctrans were almost in parallel when calculated from the results of meta-regression by the mean follow-up time. The true transformation rate was supposed to lie between the two curves, namely about 40% at the 10-year mean follow-up. Risk of malignant transformation was evaluated by the hazard ratio (HR). Pooled HRs were significantly higher in tumors with a larger pre- and postoperative tumor volume, lower degree of resection and notable preoperative contrast enhancement on magnetic resonance imaging than in others. Oligodendroglial histology and IDH mutation (IDHm) with 1p/19q codeletion (Codel) also significantly reduced the HRs. Using Kaplan-Meier curves from 8 studies with molecular data, we extracted data and calculated the 10-year malignant progression free survival (10yMPFS). The 10yMPFS in patients with IDHm without Codel was 30.4% (95% confidence interval (95%CI) [22.2–39.0]) in Htrans and 38.3% (95%CI [32.3–44.3]) in Ctrans, and that with IDHm with Codel was 71.7% (95%CI [61.7–79.5]) in Htrans and 62.5% (95%CI [55.9–68.5]) in Ctrans. The effect of adjuvant radiotherapy or chemotherapy could not be determined.