Bilateral Thalamic Gliomas Harboring Alterations of EGFR and H3K27M: An Integrated Clinicopathological Characteristics Case Series

Abstract

Bilateral thalamic gliomas (BTGs) are rare central nervous system tumors, and the outcome is usually dismal. BTG often harbors an EGFR mutation; however, a mutation in H3K27M is rare. We described 5 cases of BTGs harboring concomitant alterations of EGFR and H3K27M and retrospectively analyzed the clinicopathological features and prognosis of this rare entity. Clinical data of patients were retrieved, and immunohistochemistry and molecular analyses were performed. In addition, a systematic review of literature was conducted using PubMed. Median patient age was 6 years (range, 3-9 years). The male-to-female ratio was 3:2. Tremors and disturbed speech were the main clinical manifestations. All lesions were located at bilateral thalami, and in 3 of 4 patients, the more significant thalamic lesion was on the left. Two patients harbored insertion mutations in exon 20 of EGFR, 1 missense mutation in exon 7 of EGFR, and 2 EGFR amplifications. After a median overall survival of 8 months, 3 patients died as a result of tumor progression. Concomitant alterations of EGFR and H3K27M might indicate a new subtype of diffuse midline glioma, H3K27M-altered. In addition, EGFR alterations could provide potential molecular therapeutic strategies to improve the dismal prognosis of BTGs. Due to the rarity of these tumors, more cases must be collected to study the pathogenesis, treatment, and clinical outcomes of BTGs with double alteration phenotypes.