Targeted Inhibition in Pediatric MET and ALK-Altered Hemispheric Gliomas: Objective Responses Followed by Treatment Resistance.

Pediatric-type diffuse high-grade gliomas (pHGGs) tend to have a dismal prognosis. Some of these gliomas feature alterations in genes such as ROS1, ALK, MET, and NTRK1-3. Despite development of targeted agents, the therapeutic application of these agents in pHGGs is still unclear. The aim of this retrospective case series is to report the outcome of two patients with pHGGs who were treated at Arkansas Children's Hospital with targeted agents (Cabozantinib for a MET fusion in patient 1 and Lorlatinib for an ALK fusion in patient 2) with an initial, objective response followed by treatment resistance. Each diagnosis was determined based on histology, targeted tumor sequencing, and methylation profiling. In both cases, relapse occurred while on targeted inhibition. Recurrent tumor sequencing for patient 2 revealed a MET copy gain suggesting a mechanism of resistance in this patient. Pediatric high-grade gliomas with targetable alterations can show objective responses to pathway inhibition. Relapse after initial response may warrant additional surgical samples to identify new alterations which can lead to changes in therapy. Larger prospective cohorts are needed to study targeted agents in this population, and earlier integration of these agents may be beneficial.