Introduction Vascular malformations frequently contain somatic mutations of vascular endothelium. Brain arterio-venous malformations (AVMs) have been shown via surgically resected tissues to contain somatic activating mutations in the KRAS gene, coding for a GTPase controlling the mitogen activating protein kinase (MEK/MAP2K) pathway. However, many complex paediatric cranio-spinal AVMs are not amenable to surgical resection due to the high risk of bleeding. An alternative method of identifying such mutations is via a liquid biopsy. Liquid biopsy involves sampling of blood, either from the draining vein of the AVM or from a peripheral vein, to obtain circulating cell-free DNA (from necrotic endothelial cells). Liquid biopsy has been used successfully to identify mutations in peripheral body AVMs. We hypothesized that liquid biopsy would be a feasible method of identifying somatic mutations in complex paediatric cranio-spinal AVMs, including Vein of Galen Malformation.

Methods Our Paediatric AVM Somatic Mutation Study received institutional ethics approval. Enrolled paediatric patients (age </= 18 years) underwent endoluminal liquid biopsy from the draining vein of the AVM at the time of planned embolization, with matched peripheral blood samples; or via peripheral blood alone if no endovascular treatment was being undertaken. Cell-free DNA was extracted and underwent next generation sequencing (NGS) for our bespoke panel of genes associated with vascular malformations: KRAS, HRAS, NRAS, RASA1, BRAF, MAP2K1, MAP2K2, EPHB4, ACVRL1, SMAD4, ENG, GNAQ, PTEN, PIK3CA, TEK, and MAP3K3. Orthogonal confirmation of positive results was undertaken using digital droplet PCR testing. Patients with identified mutations underwent consultation with our paediatric oncology team for consideration of genotype-directed pharmacotherapy.

Results Of n=18 patients enrolled, n=11 patients had AVMs involving the cranio-spinal axis, and n=7 have completed NGS testing. At this preliminary stage, three patients have been identified with somatic mosaic mutations, all involving the KRAS gene. Patient 1 was diagnosed antenatally with Vein of Galen Malformation and underwent staged embolization as a neonate and infant. Liquid biopsy of the draining vein (via a microcatheter advanced across an AV fistula into the venous sac) identified a somatic activating mutation of KRAS (G12S). Patient 2 is a teenager with cervical spinal arterio-venous metameric syndrome who presented with progressive paraparesis and became wheelchair-dependent. Peripheral blood liquid biopsy identified a somatic KRAS mutation (G12D). They were commenced on the MEK inhibitor trametinib and after six months was walking independently. Patient 3 is a teenager with extensive deforming AVM of the nose and periorbital tissues. Draining vein liquid biopsy identified a somatic KRAS mutation (G12D). They were also commenced on trametinib and demonstrated marked reduction in AVM size and reduced pain.

Discussion Our preliminary results support our hypothesis that liquid biopsy is a feasible method of identifying somatic mutations in complex cranio-spinal AVMs. They also suggest that somatic activating KRAS mutations play a role in a variety of AVM phenotypes, including Vein of Galen Malformation. These results highlight potential use of genotype-directed pharmacotherapy for these disabling lesions.

Disclosures K. Bhatia: 1; C; Sydney Aneurysm Pty Ltd. 4; C; Sydney Aneurysm Pty Ltd. D. Lord: None. G. McCowage: None. D. Sylvester: None. J. Karpelowsky: None. G. Olsson: None. C. Bateman: None. B. Padhye: None. P. Muthusami: None. T. Krings: None. S. Kahana-Edwin: None.