Regulatory scrutiny has halted parts of Regenxbio’s gene therapy program after a patient in one study developed cancer, prompting the FDA to place holds on two trials. The agency’s action requires Regenxbio to provide additional safety data and investigator information before studies can resume, according to regulatory reports and coverage. The holds raise questions about transgene or vector‑related malignancy risk assessments and could reshape monitoring and preclinical requirements across adeno‑associated virus (AAV) and gene‑delivery programs. Sponsors, clinical investigators, and regulators will watch Regenxbio’s responses and any FDA guidance that emerges from the safety review.