Regulatory scrutiny intensified after the FDA placed tests of two Regenxbio gene‑therapy programs on clinical hold following a patient’s cancer diagnosis in one study, according to MedCity News. The action pauses human dosing and forces sponsors to reassess long‑term safety monitoring and trial design elements tied to insertional oncogenesis concerns. Clinical holds suspend enrollment and dosing until sponsors satisfy the agency on causality and mitigation. For gene‑therapy developers, such holds can derail regulatory timelines, prompt protocol amendments, and increase the evidentiary burden to demonstrate safety in rare‑disease populations.