A Patient-Reported Outcome (PRO) refers to any information about a patient’s health status that is reported directly by the patient themselves – without interpretation by a physician or another person. PROs capture the patient’s perspective on symptoms, functional status, quality of life, and treatment tolerability. In clinical research, PROs are used as primary or secondary endpoints when the patient’s perspective is central to assessing the clinical benefit of a therapy. Examples of classic PRO instruments include pain scales, health-related quality of life questionnaires, and symptom-specific rating scales. The direct patient perspective provides information that cannot be captured by clinical measurements alone, and is therefore an indispensable component of modern clinical trials.
Regulatory Significance of PROs
Regulatory authorities such as the EMA and FDA recognize PROs as valid endpoints for approval processes, provided they are methodologically sound in their development and validation. In 2009, the FDA published guidance on the development of PRO instruments for use in clinical trials (FDA Guidance on Patient-Reported Outcome Measures, 2009), which sets clear requirements for concept development, content validity, and psychometric properties. The EMA has incorporated corresponding requirements in various guidelines and reflection papers.
For regulatory relevance, a PRO instrument must demonstrate that it fully and precisely captures the concept to be measured (content validity), that it provides consistent results in stable patients (reliability), and that it differentiates between patient groups with varying degrees of severity (construct validity). Furthermore, a clinically meaningful change in the PRO score must be defined – this threshold is referred to as the Minimal Clinically Important Difference (MCID).
Development and Validation of PRO Instruments
The development of a PRO instrument follows a structured process that includes qualitative patient interviews (concept elicitation) to identify relevant concepts, cognitive pretests to check comprehensibility, and quantitative validation studies for psychometric evaluation. This process is complex and can take several years. Therefore, sponsors often rely on already validated and regulatory-accepted instruments, such as the EQ-5D for health-related quality of life or disease-specific instruments like the WOMAC for osteoarthritis.
When transferring a PRO instrument to other languages, linguistic validation is required, which goes beyond a simple translation. Back-translation, cognitive interviews with patients in the target language, and psychometric evaluations of equivalence are mandatory components. For multi-regional studies, the EMA requires valid and culturally adapted language versions for all relevant study regions.
Use in Clinical Trials
PROs are now used as study endpoints in almost all therapeutic areas. In oncology, PROs for assessing symptom burden and quality of life are an integral part of approval studies, as many therapies primarily aim at symptom control or have side effects that impact quality of life. In rheumatology, dermatology, and neurology, PROs are often primary endpoints, as objective clinical measures cannot fully capture the patient’s perspective.
Data collection is increasingly carried out using electronic PRO systems (ePRO), implemented on tablets, smartphones, or web-based platforms. ePRO enables timely data collection directly by the patient, reduces transcription errors, and allows for daily or weekly collection frequencies that would be difficult to achieve with paper questionnaires. Regulators accept ePRO, provided that equivalence to the paper format has been demonstrated or the instrument was developed electronically from the outset.
Challenges and Best Practices
A particular challenge with PROs is handling missing data. Patients who discontinue treatment due to side effects or whose condition worsens are more likely to not complete questionnaires. If these dropouts are systematically related to the treatment effect, a missing-not-at-random pattern can emerge, which can significantly bias the results. The statistical analysis plan must prospectively define methods for handling missing PRO data and include sensitivity analyses. Full-service CROs like mediconomics support the selection and validation of suitable PRO instruments, ePRO implementation, and statistical analysis of PRO endpoints in clinical trials.
In addition to the methodological quality of the PRO instrument, the training of study sites also plays an important role. Study personnel and patients must be clearly informed that PROs should be completed without influence from third parties. Any form of guidance or influence by nursing staff or investigators when completing the questionnaire can jeopardize the validity of the data. In practice, this means that patients should complete the questionnaire alone and without time pressure. In Good Clinical Practice-compliant studies, the correct collection of PRO data is regularly checked during monitoring. Furthermore, regulators recommend choosing collection times so that the patient does not respond immediately after a doctor’s consultation or treatment, as this could influence their answers. The temporal and contextual independence of PRO collection is a quality characteristic that must be considered in study design and monitoring.
Frequently Asked Questions (FAQ)
Can a PRO serve as a primary endpoint in an approval study?
Yes, provided the PRO instrument meets the regulatory requirements for validation and content validity, and the concept measured is clinically relevant for the approval claim. In indications such as chronic pain, symptomatic heart failure, or oncological palliative care studies, PROs are often the only meaningful primary endpoint.
What is the difference between PRO and Clinical Outcome Assessment (COA)?
COA is the umbrella term for all methods of collecting clinical endpoints and includes, in addition to PROs, clinician-reported outcomes (ClinRO), observer-reported outcomes (ObsRO), and performance outcomes (PerfO). PRO is therefore a subgroup of COAs and is characterized by the fact that reporting is exclusively by the patient themselves, without external influence.