ID #1023 Pseudo-Progression Following Radiotherapy For Paediatric Low-Grade Glioma: A Case Series Demonstrating Variation in Presentation, Radiological Appearances and Clinical Management.

Abstract Background Pseudo-progression (PsP) is an established radiological sequelae following radiation therapy for brain tumours including Paediatric Low-Grade Glioma (PLGG) and can be clinically challenging to differentiate from tumour progression. There is considerable variation in the management of PsP, hence we highlight the need for clear consensus guidelines and for research to better-characterise radiological and clinical manifestations of PsP for clinical decision making. Methods We present a case series of four patients diagnosed with PLGG and PsP following Proton Beam Therapy (PBT) at a large tertiary Paediatric Neuro-Oncology centre (UCLH). We define PsP as development of new or progressive contrast enhancement following PBT that stabilised or regressed without further oncological treatment. We present the clinical details, radiological details and management of PsP for each case. Results Four patients aged 13-16years old diagnosed with PLGG were included: one optic chiasm, two midbrain and one cervico-medullary junction. One patient was diagnosed with Low Grade Astrocytoma, and three with Pilocytic Astrocytoma. One patient had BRAF KIAA1549 fusion, and one BRAF-p.Tht599dup. 2 patients had non-total resection and 2 biopsy, all followed by 50.4-54 Gy PBT; none with prior/concurrent chemotherapy. Duration of follow-up ranged 17-36 months. Our 4 cases of PsP had earlier onset of symptoms (0.5-5 months) and shorter duration to radiological stabilisation (1.4-12 months) than cases reported in previous studies. One patient demonstrated the challenges of symptomatic management of PsP with long-term steroid use leading to toxicity and the need to switch to Bevacizumab. Two patients were asymptomatic and did not require treatment but more frequent surveillance scans. Conclusion The differentiation of PsP from true tumour progression is of critical importance in clinical practice. Our case series demonstrates that steroid therapy is effective for PsP. Steroid-sparing agents like Bevacizumab are also effective and should be considered early to avoid high dose steroid toxicity.