PNOC019 is a Phase I/II, single-arm study evaluating neoadjuvant and adjuvant Nivolumab in pediatric and young adult patients with recurrent or progressive high-grade glioma. Patients receive nivolumab prior to surgical resection (where feasible), followed by continued nivolumab post-operatively. The study incorporates correlative analyses to assess immune modulation within the tumour microenvironment and peripheral immune response. Primary objectives include safety, feasibility, and characterisation of immune-related biological effects. Secondary endpoints include progression-free survival (PFS), overall survival (OS), and radiographic response. The study aims to evaluate whether neoadjuvant checkpoint inhibition enhances anti-tumour immune activity and improves clinical outcomes in this patient population.