[Diffuse midline gliomas with H3K27 alteration in children: a clinicopathological analysis of forty-one cases]

Objective: To investigate the clinicopathological features of pediatric diffuse midline glioma with H3K27 alteration and to analyze their relationship with prognosis. Methods: Forty-one cases of childhood diffuse midline glioma with H3K27 alteration were collected at Children's Hospital of Fudan University (39 cases) and Xi'an Children's Hospital (2 cases), from July 2016 to July 2020. The clinical manifestations, imaging data, histopathology, immunohistochemical phenotype and molecular genetics features, tumor size, site and histological grading were evaluated. Results: Among the 41 cases, 21 were males and 20 females, the age of onset was 3-14 years, the average and median age was 7.6 years and 7.0 years, respectively. The tumor sites were brain stem (n=36) and other locations (n=5). The clinical manifestations were dizziness, gait disturbance, and limb weakness, etc. The MRI features were variable. The histology varied from low-grade to high-grade glioma with neuron differentiation. Immunohistochemistry showed that the tumor cells expressed H3K27M, GFAP, and Olig2. Genetic study showed that 76% (16/21) of tumors had H3F3A gene mutation, mostly accompanied by TP53 (62%, 13/21) missense mutation; five tumors (24%, 5/21) had HIST1H3B gene mutation, accompanied by missense mutations in ACVR1 and PI3K pathway-related gene PIK3CA (4/5) and PIK3R1 (1/5) mutations. The prognosis was dismal with only one alive and others died. The average and median overall survival time was 7 months and 4 months, respectively. Cox multivariate regression analysis showed that age, tumor location, radiologically maximum tumor diameter, histologic grading, and surgical methods were not significantly associated with overall survival rate (P>0.05). Conclusions: Pediatric diffuse midline gliomas with H3K27 alteration have unique clinicopathological and genetic characteristics. The prognosis is poor. The tumor location and histopathologic grading are not related to prognosis. New specific drugs and comprehensive treatment are needed to improve the prognosis.