Modeling glioblastoma relapse in vitro: a critical journey from 2D models to organ-on-chip alternatives.

Glioblastoma (GBM) is the most aggressive primary brain tumor, characterized by high recurrence rates and poor prognosis despite multimodal treatment. Understanding the mechanisms underlying GBM relapse is crucial for developing more effective therapeutic strategies. In vitro relapse models provide controlled environments to investigate tumor recurrence, therapeutic resistance, and disease progression. This review explores the spectrum of in vitro models that have been established to study human GBM relapse, including 2D cultures, 3D spheroids/organoids, microfluidic and organ-on-a-chip systems. Among the key findings, it is determined that developing in vitro GBM relapse models requires the replication of longitudinal and clinically adapted treatment regimes, assessment of therapeutic efficacy under relapse conditions, and the incorporation of treatment discontinuation phases to permit tumor regrowth and relapse formation. The integration of these findings enabled the conceptualization and design of an advanced in vitro GBM relapse system, establishing a roadmap for future relapse research. By strategically employing representative GBM relapse models, researchers can both identify patient-specific therapies to prevent relapse and validate promising treatments for recurrent disease. This crucial work bridges the gap between experimental models and patient outcomes, advancing precision medicine for recurrent GBM.