Optimizing Site Feasibility in Clinical Trials for Ultra-Rare Diseases

Why Site Feasibility is Especially Crucial for Ultra-Rare Trials

In ultra-rare disease clinical trials, where eligible patient populations may be limited to only a few individuals per country—or even globally—site feasibility takes on an elevated level of importance. A misstep in site selection can lead to zero enrollment, delays, protocol amendments, or even trial failure. Sponsors cannot afford traditional high-volume approaches or selection based on historical metrics alone.

Feasibility assessments in these studies must focus on disease-specific patient availability, diagnostic capacity, investigator expertise in rare pathologies, and local regulatory familiarity with orphan drug protocols. Effective feasibility processes enable targeted recruitment, reduced site burden, and streamlined regulatory navigation. Agencies like the EMA and FDA expect robust documentation showing rationale behind site selection for such sensitive research populations.

Challenges in Identifying Feasible Sites for Ultra-Rare Conditions

Key challenges in site feasibility include:

• Scattered patient populations: Patients may be spread across countries or continents
• Limited diagnostic infrastructure: Especially for genotypically defined subgroups
• Low investigator experience: Physicians may have managed only 1–2 cases ever
• Ethical and regulatory complexity: Local authorities may lack rare disease trial precedents

For example, in a lysosomal storage disorder trial targeting 12 global patients, one high-profile academic site failed to enroll due to lack of genetic testing facilities, despite clinical interest. Early feasibility vetting could have flagged this mismatch.

Steps in Conducting Rare Disease Feasibility Assessments

A structured feasibility process for ultra-rare studies involves:

1. Feasibility Questionnaire: Tailored to assess site’s access to target population, diagnostic tools, and previous rare disease experience
2. Patient Funnel Analysis: Estimating the number of patients diagnosable, consentable, and willing to participate within study timelines
3. Protocol Complexity Assessment: Determining alignment between study demands and site capabilities (e.g., need for sedation MRI, long-term follow-up)
4. Regulatory Landscape Review: Understanding IRB timelines, import/export rules, and pediatric approval pathways
5. Site Qualification Visits (SQVs): Virtual or on-site walkthroughs for infrastructure and PI engagement evaluation

These steps, executed sequentially, provide a risk-profiled site readiness score and inform go/no-go decisions with clarity.

Patient Mapping and Registry Utilization

Feasibility should include proactive engagement with national rare disease registries, patient advocacy groups, and reference centers. Mapping where patients are diagnosed, managed, and treated—not just where hospitals exist—is critical.

For instance, India’s Clinical Trial Registry and national disease registries can help sponsors assess where most of the genetically confirmed cases are clustered. Such data may suggest partnerships with local genetic labs or patient support NGOs to ensure effective outreach during recruitment.

Case Study: Multi-National Feasibility for a Pediatric Enzyme Replacement Trial

A sponsor planning a global trial for a pediatric metabolic disorder with 18 patients worldwide began by distributing a standard feasibility questionnaire. Despite 30 responses, only 8 sites could confirm access to more than 1 patient, and only 4 had proven ERT experience. Post-screening, 5 were qualified through remote SQVs. This focused approach led to 95% of planned enrollment in under 8 months.

Such precision feasibility ensured optimal site-to-patient ratio, regulatory readiness, and engagement from experienced clinicians—drastically reducing trial risk.

Feasibility in Decentralized or Hybrid Trial Models

Decentralized trial (DCT) elements are gaining traction in rare disease research. Feasibility must now include assessment of:

• Telemedicine infrastructure for follow-ups
• Home health visit availability for sample collection or infusions
• Local lab capabilities for urgent assessments
• eConsent and remote monitoring readiness

Ultra-rare disease trials may enroll just one or two patients per site—making hybrid or DCT components not just helpful but essential for trial execution.

Regulatory Expectations and Documentation

Agencies such as EMA, FDA, and PMDA expect site selection to be justified in the Clinical Trial Application (CTA) dossier. Key documents include:

• Site feasibility reports and questionnaires
• Rationale for geographic distribution of sites
• Documentation of site capabilities for protocol-specific procedures
• Backup site lists and criteria for substitution

During GCP inspections, regulators may question why non-performing sites were selected or why local approvals were delayed. A clear feasibility traceability matrix helps defend site selection rationale.

Conclusion: Precision Feasibility is a Cornerstone of Rare Disease Trial Success

In ultra-rare clinical trials, each patient is precious—and each site is strategic. A well-executed feasibility process minimizes trial risk, optimizes resource use, and accelerates timelines. Sponsors should invest in tailored feasibility assessments that go beyond numbers and focus on true site readiness for complex, high-stakes research.

From infrastructure and personnel to patient access and regulatory history, every data point matters. Precision in feasibility leads to precision in outcomes—both scientific and operational.

Smart Site Selection Strategies for Rare Disease Clinical Trials

Why Site Selection Matters More in Rare Disease Trials

Site selection is a critical determinant of success in any clinical trial, but its importance multiplies in rare disease studies. With limited eligible patient populations and a scarcity of experienced investigators, each site must be carefully chosen to balance enrollment potential, data quality, and operational efficiency.

Unlike large-scale trials for common conditions, rare disease trials often cannot afford the luxury of underperforming sites. A single patient enrolled or missed could significantly impact timelines, cost, and regulatory submission. Therefore, optimizing site selection is both a strategic and operational imperative in orphan drug development.

Core Criteria for Selecting Sites in Rare Disease Trials

When evaluating potential sites for rare disease research, sponsors and CROs must go beyond basic infrastructure checks. Key criteria include:

• Access to patients: Does the site have a history of treating the target rare condition or access to relevant patient registries?
• Investigator expertise: Are investigators trained in the nuances of the disease, its progression, and endpoints?
• Past performance: Has the site delivered strong enrollment and data quality in similar or related studies?
• Operational readiness: Can the site manage protocol complexity, long-term follow-up, and uncommon assessments?
• Regulatory experience: Does the site understand GCP, IRB processes, and rare disease-specific documentation?

Incorporating a weighted scorecard approach can help rank candidate sites using both quantitative and qualitative inputs.

Leveraging Centers of Excellence and Referral Networks

Many countries have established rare disease centers of excellence—clinics or hospitals that serve as regional or national referral hubs. These sites often have:

• Dedicated staff familiar with the rare condition
• Patient databases or registries linked to diagnosis codes
• On-site diagnostic capabilities like genetic testing or biomarkers
• Established relationships with advocacy groups or foundations

Examples include the EU Clinical Trials Register which lists trials conducted at specialized European reference networks (ERNs). Collaborating with such centers can accelerate enrollment and improve protocol adherence.

Geographic Strategy: Balancing Access and Feasibility

Country and region selection can make or break a rare disease trial. Important considerations include:

• Prevalence hotspots: Some rare conditions are more common in certain ethnic groups or geographic clusters.
• Regulatory timelines: Select regions with streamlined approvals for orphan drug trials.
• Health system integration: Favor countries with centralized health systems that track rare disease diagnoses.
• Language and culture: Ensure patient materials and consent forms are locally appropriate and understandable.

A hybrid approach—combining 2–3 high-enrolling countries with smaller niche sites—often delivers the best risk-adjusted outcome.

Feasibility Assessments Tailored to Rare Diseases

Traditional feasibility questionnaires often fall short in rare disease trials. Instead, consider using customized templates that assess:

• How many patients with the condition were treated in the last 12 months
• Whether the site participates in relevant registries or consortia
• Previous experience with long-term follow-up or post-marketing trials
• Availability of storage for rare biospecimens or specialized equipment

Direct feasibility interviews or virtual site visits can add qualitative depth, especially for new or non-traditional sites.

Case Study: Site Selection for an Ultra-Rare Neuromuscular Disease

A biotech company planning a Phase II trial in a neuromuscular disorder affecting fewer than 5,000 patients globally faced significant challenges. The team:

• Mapped global prevalence using registry and insurance claims data
• Identified 18 potential sites across 5 countries
• Prioritized sites with high-quality referrals from genetic counselors
• Used a 30-point feasibility scorecard including investigator interest and patient travel support

Outcome: The study exceeded its enrollment goal 2 months ahead of schedule with only 12 activated sites—saving nearly $1M in operational costs.

Mitigating Risk with Backup and Satellite Sites

Given the high stakes, sponsors should always identify backup sites early in the planning process. In parallel, consider:

• Satellite clinics: Smaller locations tied to a central site but capable of performing limited procedures
• Mobile visits: For home-based follow-ups or specialized assessments like pulmonary function or neurological exams
• Remote data capture: ePROs and decentralized tools to widen geographic reach

This flexibility helps overcome unexpected hurdles like delayed IRB approvals, investigator turnover, or site dropouts.

Conclusion: Strategic Site Selection is Central to Rare Disease Trial Success

In rare disease clinical trials, every site counts. A few well-chosen, well-supported sites with access to the right patients and expertise can be more valuable than dozens of less-prepared locations. Strategic site selection—grounded in patient access, operational readiness, and local expertise—reduces risk, accelerates timelines, and ensures high-quality data.

As rare disease research continues to evolve, sponsors who invest in smarter site strategies will not only improve trial efficiency but also build lasting relationships with the clinical centers and communities that drive orphan drug development forward.