FDA introduces Rare Disease Evidence Principles to guide therapy development

The US Food and Drug Administration (FDA) has introduced the Rare Disease Evidence Principles (RDEP), a framework to bring greater clarity and predictability to the approval of therapies for very small patient populations with serious unmet medical needs caused by known genetic defects. By broadening the types of evidence that can be considered, the initiative seeks to ease the path for drug development in rare conditions where traditional trial designs are often impractical. 

Drug development in rare diseases poses distinctive challenges. Very small patient populations can make it difficult to generate the substantial evidence of safety and effectiveness normally required through multiple, traditional clinical trials. The RDEP provides an alternative pathway, offering sponsors clearer guidance on the types of evidence that may be used to meet statutory requirements.  

“Drug developers – and the patients they hope to treat – deserve clear, consistent information from the FDA,” commented FDA Commissioner Marty Makary, MD, MPH “These principles ensure that FDA and sponsors are aligned on a flexible, common-sense approach within our existing authorities, and that we incorporate confirmatory evidence to give sponsors a clear, rigorous path to bring safe and effective treatments to those who need them most.” 

Developed jointly by the Center for Drug Evaluation and Research (CDER) and the Center for Biologics Evaluation and Research (CBER), the RDEP acknowledges the limitations of conventional study designs in rare conditions. Sponsors accepted into the process may be able to establish substantial evidence of effectiveness based on a single adequate and well-controlled trial, supported by confirmatory data. This may include strong mechanistic or biomarker data, findings from non-clinical models, clinical pharmacodynamic findings, case reports, expanded access data, or natural history studies. This flexible approach aims to ensure that the unique realities of rare disease research, such as limited patient numbers and urgent medical need, are fully considered during regulatory review. 

To qualify for the RDEP, therapies must specifically address the underlying genetic defect responsible for the condition and meet several key criteria: 

• Target a very small US patient population, generally fewer than 1000 people
• Treat diseases that lead to progressive deterioration, disability, or death
• Lack adequate alternative therapies

Sponsors must apply before initiating a pivotal trial, with each request tied to a specific protocol. Early dialogue with FDA reviewers is encouraged to define what data will be required, with patient and expert input welcomed throughout the process. 

To maintain consistency, CDER and CBER review teams will consult with the Rare Disease Policy and Portfolio Council (RDPPC) before accepting a therapy into the process. For rare cancer drugs, sponsors are advised to consult with the Oncology Center of Excellence or relevant oncology divisions to determine whether the RDEP applies. 

While RDEP provides a pathway for greater flexibility, drugs approved through the process may still be subject to postmarketing requirements to further evaluate safety and effectiveness. The RDEP framework operates separately from orphan-drug designation under section 526 of the Federal Food, Drug, and Cosmetic Act. A drug reviewed under RDEP does not automatically qualify for orphan status, and sponsors seeking orphan designation must follow the established procedures under section 526 and related regulations. 

By clarifying the types of evidence that can support approval, the FDA aims to make rare disease drug development more viable while upholding statutory standards for safety and efficacy. The framework is expected to provide sponsors with a clearer roadmap and patients with faster access to potential new therapies. As Makary noted, the ultimate goal is to ensure that rare disease populations – often among the most underserved – have a transparent and scientifically rigorous path to treatment.