Tumor Treating Fields and the Glioblastoma Microenvironment: Mechanistic Convergences with Radiotherapy

Glioblastoma (GBM) remains the most lethal primary brain tumor in adults, with a median overall survival of approximately 15–20 months despite multimodal treatment including surgery, chemoradiation, and Tumor Treating Fields (TTFields). While the survival benefit of TTFields was established by the EF-14 phase III trial, their biological effects extend well beyond the canonical anti-mitotic mechanism and encompass extensive interactions with the GBM tumor microenvironment (TME). This review provides an integrated mechanistic analysis of TTFields–TME interactions in GBM, with a distinctive focus on their convergence with radiotherapy. We examine how TTFields activate innate immune sensing through cGAS/STING and AIM2 inflammasome pathways, drive immunogenic cell death, reprogram tumor-associated macrophages, and prime adaptive T cell responses. We further address TTFields effects on glioma stem cells, blood–brain barrier permeability, and intracellular signaling governing invasion, angiogenesis, and autophagy. Critically, we develop the mechanistic and clinical case for TTFields-radiotherapy combinations, highlighting convergent mechanisms of DNA repair impairment, mitotic catastrophe, and innate immune activation. Practical considerations for concurrent clinical implementation are discussed alongside a research agenda centered on optimal timing, hypofractionation, and predictive biomarkers. Available evidence—largely preclinical—suggests that TTFields may act as a TME-remodeling platform whose potential is most likely to be realized through mechanistically informed combinations.