Presentation (CTI)

OBJECTIVES: For orphan drugs, small patient populations often constrain evidence generation, making regulatory standards a key determinant of approval success. This study examines how differences in evaluation of submitted evidence shapes authorization outcomes across the US FDA, EMA and Health Canada (HC).
METHODS: A structured review identified orphan regulatory decisions issued between 2023 and 2025. Three therapies with divergent outcomes were selected as case studies: palovarotene for Fibrodysplasia Ossificans Progressiva, lifileucel for advanced Melanoma, and arimoclomol for Neimann-Pick disease (type C). Publicly available assessment reports were reviewed on trial design, use of external or natural history comparators, endpoint selection, analytical approaches, and stated approval, refusal, or withdrawal rationales.
RESULTS: Across all three case studies, regulatory evaluations diverged in how agencies weighed evidentiary uncertainty. The FDA consistently prioritized unmet need, accepting single-arm trials, intermediate/surrogate endpoints, and modest treatment effects to support accelerated approval. Post-authorization risk was mitigated through boxed warnings, label restrictions, and confirmatory evidence requirements. In contrast, the EMA required key uncertainties to be resolved prior to regulatory authorization, requiring randomized study designs and pre-specified analysis of clinical endpoints. These standards were not met for any of the case studies, resulting in refusal for palovarotene and withdrawal of the lifleucel and arimoclomol submissions. HC adopted an intermediate position, granting conditional approval for palovarotene and lifleucel stating unmet need, but explicitly linking approval to submission of confirmatory evidence.
CONCLUSIONS: Variations in orphan drug regulatory outcomes reflect how regulators manage evidentiary and methodological uncertainty rather than differences in the underlying evidence. Aligning global evidence generation strategies with these regional standards is critical for mitigating pitfalls and enabling coordinated global approvals.