# Phase 1, 2 and 3 trials

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

## TL;DR

The three stages a new drug passes through: phase 1 finds a safe dose in a few dozen patients, phase 2 looks for signs of activity in a hundred or so, and phase 3 compares it with the standard treatment in hundreds or thousands.

## Summary

Phase 1 escalates the dose in small groups until side effects limit it, defining the maximum tolerated dose and the dose for later study; in oncology, phase 1 patients have usually exhausted standard options and modern phase 1 trials often expand into hundreds of patients with early efficacy readouts. Phase 2 tests the chosen dose for response in a specific cancer, sometimes randomised and sometimes single-arm, and phase 3 is the large randomised, often blinded, comparison against the standard of care that regulators normally require for full approval. Phase 4 studies follow a marketed drug. Only around 5% of oncology drugs entering phase 1 reach approval, and around a third of phase 3 trials fail, which is a major driver of drug cost.

## Fields

- Kind: Term
- Last checked: 2026-09-09
- Also known as: phase 1; phase 2; phase 3; phase I; phase II; phase III; phase 1/2; phase I/II; phase 2/3; phase II/III; phase 4; phase IV; first-in-human; first in human; dose-escalation; dose escalation; dose-finding; pivotal trial; pivotal trials; pivotal; registrational; confirmatory trial; confirmatory trials; early-phase; early phase; late-phase; late phase; late-stage trial; late-stage trials

## Sources

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

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JSON: https://onco.cc/api/v1/entities/trial-phases.json