Infant-Type Hemispheric Glioma With NTRK Fusion Responds to Larotrectinib.

Infant-type hemispheric glioma is a distinct form of high-grade glioma occurring in infancy and early childhood. It arises in the cerebral hemispheres and is characterized by recurrent molecular alterations involving genes such as NTRK, ROS1, MET, and ALK. We present the case of a four-month-old infant with a large solid-cystic parietal-occipital hemispheric mass. Histologic examination revealed a cellular, poorly differentiated tumor with areas of necrosis and prominent desmoplasia. DNA methylation profiling supported classification as infant-type hemispheric glioma, and next-generation sequencing identified a TPM3::NTRK1 fusion. An integrated diagnosis of infant-type hemispheric glioma was made. Following surgical resection, targeted therapy with an NTRK inhibitor was initiated, resulting in a sustained clinical and radiologic response. This case underscores the importance of integrated histologic and molecular evaluation in establishing the diagnosis and guiding management of these tumors, as well as the clinical relevance of identifying targetable alterations.