Thalamic high-grade gliomas in children: a distinct clinical subset?

Abstract

Pediatric high-grade gliomas (HGGs) of the thalamic region account for up to 13% of pediatric HGGs and usually result in only anecdotal long-term survival. Because very little is known about these tumors, we aimed to further characterize them. In our series of 99 pediatric thalamic HGGs, there were no significant differences in survival between patients with tumors affecting the thalamus alone (including bithalamic lesions) and patients with tumors affecting the thalamus plus adjacent structures. Tumor resection (event-free survival/overall survival) and an early treatment response to radiotherapy/chemotherapy (event-free survival) had independent prognostic significance, as shown by Kaplan-Meier and multivariate Cox regression analyses. When we compared clinical characteristics and outcomes of pediatric thalamic HGG with those of pediatric (nonthalamic) supratentorial (n = 177) as well as pediatric pontine HGG (including diffuse intrinsic pontine gliomas; n = 234), we found that thalamic HGG shared more similarities with pontine than with supratentorial HGG, but overall, it appeared to represent a clinically distinct subgroup of pediatric HGG. The varying extent of tumor resection in the different tumor localizations may play some role in the observed clinical differences, as shown by multivariate Cox regression analyses, but the tumor site itself was also identified as an independent prognostic parameter. Thus, an additional location-specific effect on survival and/or tumor biology, despite different neurosurgical accessibility, has to be considered. Therefore, future investigations should try to further characterize the obviously site-specific heterogeneity of pediatric HGG on a molecular genetic basis.

Fig. 1.

Kaplan-Meier analysis of event-free survival (A) and overall survival (B) in pediatric patients with thalamic high-grade gliomas, with respect to their treatment response evaluation at week 8. Differences between the various subgroups were significant for the comparison of event-free survival between the patient group with complete response (CR) versus the one with progressive disease (PD), the one with PD versus the one with partial response (PR), and the one with PD versus the one with stable disease (SD). There was also a significant difference for the comparison of overall survival between the patient group with CR versus the one with PD.

Fig. 2.

Kaplan-Meier analysis of event-free survival (A) and overall survival (B) in pediatric patients with thalamic, pontine, and (nonthalamic) supratentorial high-grade gliomas (HGGs). Differences between the various subgroups were all significant, except for the comparison of event-free survival between the thalamic and pontine HGGs.