Two independent reports showed serial, longitudinal tumor sampling in recurrent glioblastoma (rGBM) exposes therapy effects and immune responses that standard MRI failed to reveal. Break Through Cancer’s TeamLab and Mass General Brigham teams analyzed repeated biopsy cores and multi‑omics data to uncover deep immune activation and pharmacodynamic signatures during oncolytic virus and immunotherapy trials. One study demonstrated CAN‑3110 (an oncolytic virus) triggered profound intratumoral immune responses not evident on routine clinical analyses; another multi‑institutional paper in Science Translational Medicine concluded that longitudinal biopsies are safe, feasible, and captured therapeutic effects invisible to MRI—including pharmacodynamic markers of target engagement. The findings establish serial biopsy as a tool to de‑risk clinical development by providing direct tumor‑level readouts of mechanism and response, informing trial design and regulatory endpoints in GBM and other CNS immunotherapy studies.