Teams at Mass General Brigham, Harvard Medical School and Break Through Cancer reported that serial, longitudinal tumor biopsies in patients with recurrent glioblastoma exposed deep intratumoral immune and pharmacodynamic responses to therapy that routine MRI failed to detect. Detailed multi‑omics from oncolytic virus and immunotherapy‑treated cores showed profound, spatially restricted immune activation and drug engagement not evident in imaging or clinical metrics, according to Science Translational Medicine and a Break Through Cancer TeamLab release. Leads including E. Antonio Chiocca and collaborators concluded longitudinal biopsy is feasible and safe in rGBM, and that serial sampling can capture early pharmacodynamic effects, immune infiltration, and tumor changes that MRI may misclassify as progression or pseudoprogression. The findings suggest serial biopsy could refine endpoint selection and accelerate development of immunotherapies for brain tumors, while raising practical questions about biopsy logistics, patient selection, and regulatory acceptance.