Endpoints and Surrogate Outcomes

#What did the trial measure?

An endpoint measures an outcome in a trial. Clinical outcomes can directly describe whether people feel better, function better or live longer. A report needs to explain what was measured and what change would mean for the question being studied.

A protocol can identify the primary outcome before results are known. CONSORT emphasizes access to the protocol and analysis plan because these help readers assess the report and notice undeclared changes. Read the planned outcome alongside the reported result.

Evidence: FDA: Surrogate endpoint resources / CONSORT 2025 explanation and elaboration

#A surrogate is a substitute, not the benefit itself

A surrogate endpoint is used instead of a direct measure of how a patient feels, functions or survives. It may allow a shorter or more practical study, but it does not measure the clinical benefit of primary interest by itself.

A biomarker can have several roles, including identifying participants, monitoring safety or measuring a biological response. Being a biomarker does not automatically make it a validated substitute for a clinical outcome.

Evidence: FDA: Surrogate endpoint resources

#Validation depends on the context

FDA describes candidate, reasonably likely and validated surrogate endpoints. A validated surrogate has a mechanistic rationale and clinical evidence that an effect on it predicts a specific clinical benefit. A candidate surrogate is still being evaluated.

A reasonably likely surrogate has supporting rationale but insufficient clinical data to count as validated. FDA may use this category for accelerated approval, with continued evaluation needed afterward. Do not turn a marker change into a stronger claim about benefit than its evidence supports.

Evidence: FDA: Surrogate endpoint resources

#Read benefits and harms together

Even a useful endpoint does not answer every question about a treatment. FDA describes assessment of clinical benefit alongside adverse effects. Ask whether the endpoint reflects the benefit that matters to the patient and what other outcomes or harms remain uncertain.

The practical reading questions are: what was the endpoint, why was it chosen, what evidence supports a surrogate in this setting, and how does the result relate to benefits and harms? This page is general research literacy, not advice about an individual treatment.

Evidence: FDA: Surrogate endpoint resources / CONSORT 2025 explanation and elaboration

Source note

The sections above were checked against the linked sources. No clinical review has been performed. This is general research education, not a clinical guideline.