The FDA’s expedited review for Stealth BioTherapeutics’ Barth syndrome therapy signals a regulatory shift benefiting rare disease treatments. Following multiple delays and rejections, a planned decision in September reflects renewed agency urgency amid public and congressional advocacy. Concurrently, the FDA’s controversial rejection of Replimune’s melanoma drug has cascading industry effects, including trial shutdowns by other biotechs, evidencing shifting regulatory dynamics affecting cancer and rare disease drug development.