Objectives To understand the risk factors for and patterns of progression of low grade glioma (LGG).

Design Single centre retrospective cohort study.

Subjects Patients undergoing at least two neurosurgical procedures for LGG, the first being for diffuse LGG (WHO 2). 22 patients included (14M; 8F); mean age at time of first operation 37.7±2.7 years. 20 patients had a Performance Status (PS) 0–1 and 2 patients had a PS 2.

Methods All patients with LGG diagnosed in between 2009–2018 were retrospectively evaluated. Variables of interest included demographics, staging, performance status, time to re-operation (TTR), extent of resection, molecular genetics (1p19q co-deletion, IDH status). Tumour volumes were estimated from MRI images by the validated ABC/2 equation. Statistical analyses were performed by Stata13.0.

Results The tumour progressed in WHO grade in 18 patients (WHO grade 3 (n=15); WHO grade 4 (n=3). Mean time to re-operation after the first surgery was 7.0±1.2 years following gross total resection (GTR) and 3.2±0.7 years following subtotal resection (STR). Non-adjusted analysis of risk factors for time to re-operation (TTR) showed absence of 1p19q co-deletion as a risk factor (p=0.021). Adjusted analysis revealed that GTR, 1p19q mutation, PS 0 at 1 st surgery and tumour volumetric change decrease the risk for re-intervention (p<0.05). Chemo-radiotherapy was not associated with TTR.

Conclusions In our cohort, TTR in LGG was influenced by the amount of initial resection, 1p19q deletion, PS and post-operative volumetric change.