Abstract INTRODUCTION Low-grade gliomas (LGG) present 10-year overall survival rates of 90%. However, many require multiple lines of treatment. Bevacizumab/Irinotecan is the standard third line treatment for recurrent LGG in the UK; with targeted therapies being accessible only as a fourth or subsequent line for most cases. Access to targeted therapies may also be limited by the need for tumour tissue, which isn’t always available for LGG cases. Bevacizumab is effective in LGG, but between 65 and 90% regrow within 5-8 months from treatment discontinuation [Hwang 2013; Green 2023]. In this context and based on preliminary evidence from the group in Marseille (France) [Heng, 2016; Roux 2021], we explored if Vinblastine could extend the progression-free survival (PFS) after Bevacizumab. METHODS Institutional review of patients aged 1-25 years with relapsed LGG treated between 2018 and 2022 with Bevacizumab/Irinotecan followed by Vinblastine (24 weekly doses) at the discretion of the treating physician. The primary endpoint was PFS post-Bevacizumab (PFS-pB) measured at 8 months from last dose of Bevacizumab to allow for comparison with the results of a recently published national case series of paediatric LGG treated with Bevacizumab-based regimes [Green 2023]. RESULTS Ten LGG cases received Bevacizumab/Irinotecan. One progressed on treatment, leaving 9 evaluable (8 completed 12 cycles, 1 discontinued treatment due to toxicity): of which 6 received Vinblastine. The PFS-pB at 8 months was 66% (4/6) with Vinblastine vs 35% in the national UK case series. CONCLUSIONS In this limited case series, Vinblastine delayed tumour progression following completion of Bevacizumab-based regimes compared to a national UK case series. Vinblastine could be considered as a holding strategy after Bevacizumab where targeted therapies are not readily available. Further prospective studies are required to validate this hypothesis.

LGG-47. VINBLASTINE TO PREVENT TUMOUR REBOUND AFTER BEVACIZUMAB/IRINOTECAN IN CHILDREN AND ADOLESCENTS WITH MULTIPLY RELAPSED LOW-GRADE GLIOMAS: THE SOUTH LONDON PAEDIATRIC &amp; TYA NEURO-ONCOLOGY NETWORK EXPERIENCE

LGG-47. VINBLASTINE TO PREVENT TUMOUR REBOUND AFTER BEVACIZUMAB/IRINOTECAN IN CHILDREN AND ADOLESCENTS WITH MULTIPLY RELAPSED LOW-GRADE GLIOMAS: THE SOUTH LONDON PAEDIATRIC &amp; TYA NEURO-ONCOLOGY NETWORK EXPERIENCE

LGG-47. VINBLASTINE TO PREVENT TUMOUR REBOUND AFTER BEVACIZUMAB/IRINOTECAN IN CHILDREN AND ADOLESCENTS WITH MULTIPLY RELAPSED LOW-GRADE GLIOMAS: THE SOUTH LONDON PAEDIATRIC & TYA NEURO-ONCOLOGY NETWORK EXPERIENCE