# Primary, secondary and co-primary endpoints

Source: https://onco.cc/terms/primary-endpoint/  
OnCo record `primary-endpoint` (Term). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

The primary endpoint is the single measurement a trial is designed and sized to test, declared in advance; if it is met, the trial is 'positive'. Secondary endpoints are additional measures that can support but not rescue a trial that missed its primary.

## Summary

Common oncology primary endpoints are overall survival, progression-free survival (often by blinded central review), event-free or disease-free survival, objective response rate, and pathological complete response; dual or co-primary endpoints (PFS and OS) split the type I error between them with hierarchical testing. A trial that misses its primary but shows a survival trend is 'technically negative' (BILCAP, JAVELIN Ovarian) and regulators rarely approve on secondary endpoints alone. Endpoint choice shapes approval speed (surrogates are faster) and interpretation, and changing the primary endpoint mid-trial, or reporting a secondary as if it were primary, are recognised warning signs.

## Fields

- Kind: Term
- Last checked: 2026-09-09
- Also known as: primary endpoint; primary end point; primary endpoints; primary outcome; secondary endpoint; secondary endpoints; key secondary; key secondary endpoint; co-primary; co-primary endpoints; dual primary; dual primary endpoints; composite endpoint; exploratory endpoint; endpoint; endpoints; met its primary endpoint; met the primary endpoint; missed its primary endpoint; positive trial; negative trial; technically negative; primary outcomes; co-primary endpoint; composite endpoints; key secondaries

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Clinical_endpoint
- Wikipedia: https://en.wikipedia.org/wiki/Clinical_endpoint

## Connected records

- terms: [Data maturity (immature vs mature survival data)](https://onco.cc/terms/data-maturity/), [Endpoint](https://onco.cc/terms/endpoint/), [Estimands and intercurrent events (ICH E9(R1))](https://onco.cc/terms/estimand/), [Event-free / disease-free survival (EFS, DFS, iDFS, RFS)](https://onco.cc/terms/efs/), [Futility analysis (stopped for futility)](https://onco.cc/terms/futility/), [Group sequential design, stopping rules and alpha spending](https://onco.cc/terms/group-sequential-design/), [ICH good clinical practice (E6)](https://onco.cc/terms/ich-gcp/), [Interim analysis, readout and data cut-off](https://onco.cc/terms/interim-analysis/), [Objective response rate (ORR)](https://onco.cc/terms/orr/), [Overall survival (OS)](https://onco.cc/terms/os/), [Pivotal (registrational) trial](https://onco.cc/terms/pivotal-trial/), [Pre-specified vs post-hoc analysis](https://onco.cc/terms/prespecified-vs-post-hoc/), [Progression-free survival (PFS)](https://onco.cc/terms/pfs/), [Statistical significance (P values, alpha, multiplicity)](https://onco.cc/terms/statistical-significance/), [Surrogate endpoint](https://onco.cc/terms/surrogate-endpoint/), [Trial protocol and statistical analysis plan](https://onco.cc/terms/trial-protocol/), [Trial registration and results reporting (ClinicalTrials.gov, EU CTR)](https://onco.cc/terms/trial-registration/)
- fronts: [Drug Discovery Platforms](https://onco.cc/fronts/drug-discovery/)

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