Brainstem and thalamic gliomas are rare, and they are poorly understood in 
adults. Genetic aberrations that occur in these tumors are still unknown. In 
this study, we investigated whether thalamic gliomas have different genetic 
aberrations and clinical outcomes compared with brainstem gliomas in adults. 
Forty-three glioma samples were selected, including 28 brainstem and 15 thalamic 
gliomas. The frequency of the K27M mutation in adult midline gliomas was 58.1%. 
High-grade gliomas in the thalamus were statistically significantly more 
numerous than brainstem gliomas. Patients with K27M mutant brainstem gliomas had 
a significantly shorter overall survival than patients with wild-type tumors (P 
= .020) by Cox regression after adjustment for other independent risk factors. 
However, there was no statistical tendency toward a poorer overall survival in 
thalamic gliomas containing the K27M mutation compared with wild-type tumors. 
The presence of the K27M mutation significantly corresponded with mutations in 
TP53 in thalamic gliomas. Interestingly, the K27M mutation was mutually 
exclusive with mutations in IDH1, which was detected only in brainstem gliomas. 
The microarray data identified 86 differentially expressed genes between 
brainstem and thalamic gliomas with the K27M mutation. The cyclin-dependent 
kinase 6 (CDK6) gene, which plays an important role in cancer pathways, was 
found to be differentially expressed between brainstem and thalamic gliomas with 
K27M mutations. Although the K27M mutation was frequently observed in adult 
brainstem and thalamic gliomas, this mutation tended to be associated with a 
poorer prognosis in brainstem gliomas but not in thalamic gliomas. Brainstem 
gliomas may present different genetic aberrations from thalamic gliomas. These 
differences may provide guidance for therapeutic decisions for the treatment of 
adult brainstem and thalamic gliomas, which may have different molecular 
targets.