Serial, multi‑omics tumor biopsies in patients with recurrent glioblastoma uncovered robust intratumoral immune and pharmacodynamic signals that MRI and routine clinical metrics missed, according to reports from Mass General Brigham and Break Through Cancer teams. Analyses from patients treated with oncolytic virus therapy CAN‑3110 revealed profound, localized immune activation deep within tumor tissue. The studies established that longitudinal biopsy sampling is feasible and safe for selected GBM patients and can reveal target engagement and immune biology that noninvasive imaging cannot. Investigators argue that serial tissue sampling can accelerate development of brain tumor immunotherapies by providing direct pharmacodynamic readouts and clarifying whether radiographic progression reflects tumor versus inflammation. The findings could reshape trial designs and regulatory endpoints for neuro‑oncology programs.