DMG-55. Extraneural Metastasis in H3K27-Altered Diffuse Midline Glioma

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Abstract H3K27-altered diffuse midline glioma (DMG) are highly aggressive tumors that can present with leptomeningeal spread and metastasis within the central nervous system (CNS). Extraneural spread of DMG outside the CNS, however, is sparsely reported and there is no consensus on management of such disease. We aimed to describe the clinical course and molecular features of pediatric DMG with extraneural metastasis. Clinical and molecular data were retrospectively collected from five institutions internationally and the frequency of genomic alterations was compared to an external multi-institution control cohort of DMGs. Six patients—3 males and 3 females presenting between ages 6 to 21 years—were included. All 6 had musculoskeletal extraneural disease. Five had disease localized exclusively to the bone, of which four (80%) had disease outside the vertebral column (pelvis in 4 patients, ribs in 2 patients, femur in 1 patient). One patient had disease in the soft tissue of the neck. Two patients (33%) had extraneural disease at diagnosis of DMG and 4 (67%) developed extraneural spread at disease progression. All patients also had disease disseminated within the CNS, with 4 patients (67%) presenting with dissemination at diagnosis and 2 (33%) developing both intra and extra-CNS disease later in their course. All primary tumors had H3K27M alteration and 4 (67%) had a TP53 mutation. In comparison, our reference cohort (n = 297) had a TP53 mutation prevalence rate of 49%. There were no other recurrent alterations in our cohort. In conclusion, we present 6 biopsy-proven cases of DMG with extraneural metastasis to the bone and soft tissue. Extraneural metastasis occurred both locoregionally (to vertebral bodies) and distantly (to ribs, pelvis, femur, and neck) suggesting both local invasion and hematogenous dissemination as potential mechanisms for spread. The presence of extraneural manifestation of DMG may impact therapy recommendations, and therefore, awareness is critical.

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