Objectives: Rare diseases are often heterogeneous in their progression and response to treatment, with only a small population for study. This provides challenges for evidence generation to support HTA, so novel research methods are required. Methods: Discussion with an expert panel was augmented with references and case studies to explore robust approaches for HTA evidence generation for rare disease treatments. Results: Traditional RCTs can be modified using sequential, three-stage or adaptive designs to gain more power from a small patient population or to focus trial design. However, such designs need to maintain important design aspects such as randomization and blinding and be analyzed to take account of the multiple analyses performed. N-of-1 trials use within-patient randomization to test repeat periods of treatment and control until a response is clear. Such trials could be particularly valuable for rare diseases and when prospectively planned across several patients and analyzed using Bayesian techniques, a population effect can be estimated that might be of value to HTA. When the optimal outcome is unclear in a rare disease, disease specific patient reported outcomes can elucidate impacts on patients' functioning and wellbeing. Likewise, qualitative research can be used to elicit patients' perspectives, with just a small number of patients. Conclusions: International consensus is needed on ways to improve evidence collection and assessment of technologies for rare diseases, which recognize the value of novel study designs and analyses in a setting where the outcomes and effects of importance are yet to be agreed.
Keywords: Patient outcome assessment, Rare diseases, Research design, Technology assessmentMedicines regulators have defined "orphan products" as those that treat patients with life-threatening or chronically debilitating "rare conditions" that have no satisfactory treatment.The classification of a "rare condition" (Table 1) differs from country to country, but all classification systems cover a wide spectrum of diverse conditions, with 5,000-8,000 rare conditions in the European Union and United States.The low prevalence of rare diseases presents the obvious challenge of paucity of patients to study, but other challenges also arise. Many rare conditions are genetic, metabolic diseases that are highly heterogeneous, so the understanding of natural history and demonstration of value of treatment at a population level is challenging. Regulators have created a range ofThe authors thank Professor Helle Ploug Hansen, Dr. Carlo Incerti, Dr. Karen Ritchie, Dr. PK Tandon, and Dr. Yot Teerawattananon for comments on a final draft of this study and to peer reviewers for comments that substantially improved this study. Karen Facey, Alastair Kent, and Durhane Wong-Rieger were part-funded by Genzyme to undertake this work by means of a research grant.initiatives to support development of orphan products, including scientific advice to help manufacturers develop study plans, conditional authorization/licen...