Paediatric Gliomas: BRAF and Histone H3 as Biomarkers, Therapy and Perspective of Liquid Biopsies

SIMPLE SUMMARY: Gliomas are major causes of worldwide cancer-associated deaths in children. Generally, paediatric gliomas can be classified into low-grade and high-grade gliomas. They differ significantly from adult gliomas in terms of prevalence, molecular alterations, molecular mechanisms and predominant histological types. The aims of this review article are: (i) to discuss the current updates of biomarkers in paediatric low-grade and high-grade gliomas including their diagnostic and prognostic values, and (ii) to discuss potential targeted therapies in treating paediatric low-grade and high-grade gliomas. Our findings revealed that liquid biopsy is less invasive than tissue biopsy in obtaining the samples for biomarker detections in children. In addition, future clinical trials should consider blood-brain barrier (BBB) penetration of therapeutic drugs in paediatric population. ABSTRACT: Paediatric gliomas categorised as low- or high-grade vary markedly from their adult counterparts, and denoted as the second most prevalent childhood cancers after leukaemia. As compared to adult gliomas, the studies of diagnostic and prognostic biomarkers, as well as the development of therapy in paediatric gliomas, are still in their infancy. A body of evidence demonstrates that B-Raf Proto-Oncogene or V-Raf Murine Sarcoma Viral Oncogene Homolog B (BRAF) and histone H3 mutations are valuable biomarkers for paediatric low-grade gliomas (pLGGs) and high-grade gliomas (pHGGs). Various diagnostic methods involving fluorescence in situ hybridisation, whole-genomic sequencing, PCR, next-generation sequencing and NanoString are currently used for detecting BRAF and histone H3 mutations. Additionally, liquid biopsies are gaining popularity as an alternative to tumour materials in detecting these biomarkers, but still, they cannot fully replace solid biopsies due to several limitations. Although histone H3 mutations are reliable prognosis biomarkers in pHGGs, children with these mutations have a dismal prognosis. Conversely, the role of BRAF alterations as prognostic biomarkers in pLGGs is still in doubt due to contradictory findings. The BRAF V600E mutation is seen in the majority of pLGGs (as seen in pleomorphic xanthoastrocytoma and gangliomas). By contrast, the H3K27M mutation is found in the majority of paediatric diffuse intrinsic pontine glioma and other midline gliomas in pHGGs. pLGG patients with a BRAF V600E mutation often have a lower progression-free survival rate in comparison to wild-type pLGGs when treated with conventional therapies. BRAF inhibitors (Dabrafenib and Vemurafenib), however, show higher overall survival and tumour response in BRAF V600E mutated pLGGs than conventional therapies in some studies. To date, targeted therapy and precision medicine are promising avenues for paediatric gliomas with BRAF V600E and diffuse intrinsic pontine glioma with the H3K27M mutations. Given these shortcomings in the current treatments of paediatric gliomas, there is a dire need for novel therapies that yield a better therapeutic response. The present review discusses the diagnostic tools and the perspective of liquid biopsies in the detection of BRAF V600E and H3K27M mutations. An in-depth understanding of these biomarkers and the therapeutics associated with the respective challenges will bridge the gap between paediatric glioma patients and the development of effective therapies.