Sponsors commonly ask one patient number to do three different jobs: describe disease prevalence, estimate protocol fit, and predict enrollment.
Those measures aren’t interchangeable.
A site may genuinely care for a large population in the target indication and still have limited enrollment capacity for a specific study. The gap emerges when that population is filtered through protocol requirements, the care pathway, competing studies, and the site’s ability to move candidates from identification through screening.
Patient availability describes the size of the potential population. Enrollment potential describes who can realistically reach enrollment within the study’s recruitment window.
Feasibility often begins with a broad population estimate: patients with the relevant diagnosis, stage, treatment history, or other characteristics.
Sponsors ultimately need a much narrower denominator.
Some patients will fail protocol-specific criteria, while others may be clinically eligible but at the wrong point in treatment. Some may receive care outside the site’s referral network, qualify for another open study, decline participation, or face visit requirements that make enrollment unlikely.
Patient availability can change considerably between site selection and active recruitment.
Eligibility may depend on where a patient is in the course of care. Progression, a new treatment, a biopsy, a procedure, or another clinical event can move someone into or out of the relevant population. The same site can therefore present a different enrollment opportunity at different points in the study.
For sponsors, this makes timing part of feasibility. A patient estimate gathered months before activation may still be useful, but it shouldn’t be treated as a fixed representation of the population available when recruitment begins.
The better assessment considers not only how many potentially relevant patients a site serves, but also how often patients are likely to enter the eligibility window during the enrollment period.
A strong patient pool only creates enrollment opportunity if the site can move candidates through the recruitment process fast enough.
Coordinator bandwidth, investigator involvement, referral behavior, chart-review demands, scheduling, and protocol-specific procedures all influence screening throughput. These factors determine how many potential candidates the site can evaluate while they remain relevant to the study.
That creates an operational ceiling. A site may have substantial patient access but limited capacity to review, contact, and screen those patients within the enrollment window.
Sponsors evaluating site potential therefore need to consider both sides of the equation: the size of the addressable population and the site’s ability to convert that population into completed screening activity.
Concurrent studies can draw from the same patient population while also competing for coordinator time, investigator attention, diagnostic capacity, and treatment resources.
That changes how sponsors should interpret patient availability. A site may appear to have a strong population for a new study, but part of that population may also qualify for another open protocol or may be less accessible because the site’s research infrastructure is supporting several studies at once.
The usable pool is therefore smaller than the total disease population. Sponsors need to consider how much of that population is actually available to this study during its recruitment window, given the site’s existing trial portfolio and operational demands.
For sponsors, stronger site intelligence connects patient availability with the conditions required to convert that opportunity into enrollment.
That means looking beyond a single population estimate and examining protocol fit, timing, referral patterns, competing studies, screening throughput, and site capacity together.
Patient counts still belong in feasibility. They just should not be asked to predict enrollment on their own.
Third Opinion helps research-focused practices enroll more patients, onboard more studies, and fulfill industry data requests while giving patients the opportunity to participate in potentially life-saving treatments. Founded by physicians, Third Opinion is built for patients and researchers.
Contact Third Opinion for more information.