Clinico-pathological and molecular characterization of diffuse midline gliomas: is there a prognostic significance?

H3K27M mutant diffuse midline gliomas (DMGs) are considered grade IV irrespective of histological features and have dismal prognosis. We evaluated clinico-pathologic, radiological, and molecular characteristics of DMGs across all ages.

One twenty-six DMGs were identified over 10 years. Immunohistochemistry was done for H3K27M, ATRX, IDH1, and p53, and Sanger sequencing performed for IDH1 and H3K27M mutation. Patient demographics and clinico-radiologic characteristics were reviewed and survival analysis performed.

DMGs comprised 5.3% of all gliomas with 49.2% H3K27M mutant and 50.8% wild types. Majority (75.68%) of pediatric and 38.20% of adults were H3K27M mutant (p = 0.0001). Amongst H3K27M mutants, brainstem (46.43%) was the commonest location in pediatric and thalamus (61.76%) in adults. H3K27M mutation was mutually exclusive with IDH mutation in 93.55%, while p53, ATRX mutation were seen in 56.4% and 30.6% cases respectively. Software-based immunohistochemistry evaluation (H-scoring) showed 99.2% concordance with sequencing for H3K27M mutation. Radiologically, no significant difference in contrast enhancement was seen between mutant and wild types (p = 0.05). The difference in overall survival (OS) was not significant in mutant versus wild types, with age or location. Tumor resection independently and on correlation with H3K27M did not influence OS (p = 0.51 and p = 0.47). Adjuvant therapy impacted survival significantly in adults (p = 0.0009), however, not in pediatric cases (p = 0.06).

The study highlights the differences in frequency and location of pediatric and adult DMGs. IHC (H-scoring) for H3K27M mutation is an excellent surrogate for sequencing. Prognosis remains dismal irrespective of age, location, and H3K27M status. Potential therapeutic targets need to be explored.