Clinical Trial Phases Explained: From First-in-Human to Confirmation

Phase 1: Safety and Dose

A phase 1 trial is the first time a drug is given to people, usually a small number of patients across several dose levels. The primary goals are to characterise safety, identify dose-limiting toxicities and establish a recommended dose for further study.

Anti-tumour activity is recorded but is not the main endpoint, and phase 1 populations are often heavily pre-treated and heterogeneous. Response rates from phase 1 can be promising or misleading and need confirmation.

Phase 2: Preliminary Efficacy

Phase 2 trials test the recommended dose in a more defined population, often a single tumour type or biomarker-selected group, to estimate response rate and progression-free survival and to refine the safety picture.

Many phase 2 trials are single-arm, meaning there is no direct comparison group. This makes it hard to know how much of the observed benefit is due to the drug versus patient selection.

Phase 3: Confirmation Against Standard of Care

Phase 3 trials randomise larger numbers of patients between the new treatment and the current standard, with endpoints such as overall survival or progression-free survival assessed by blinded review.

Randomisation is what allows a causal claim that the new treatment is better. A positive phase 3 trial is generally what supports a change in practice and full regulatory approval.

How Modern Designs Blur the Lines

Expansion cohorts within a large phase 1 study can generate the efficacy data that once required a separate phase 2, and some drugs for rare biomarker-defined groups have been approved on the basis of such data.

Basket trials test one drug across many tumour types sharing a biomarker; umbrella trials test several drugs within one tumour type by biomarker; adaptive designs change allocation as data accrue. These improve efficiency but require careful interpretation.

Reading Trial Evidence

Key questions for any trial result: was there a randomised comparator, what was the primary endpoint and was it met, how large was the effect and its confidence interval, and how similar is the trial population to the patient in front of you.

Accelerated approvals based on surrogate endpoints such as response rate are provisional and depend on later confirmatory trials, which occasionally fail.

Key Takeaways

• ·Phase 1 is about safety and dose; anti-tumour activity is secondary.
• ·Phase 2 estimates efficacy, often without a comparator arm.
• ·Phase 3 randomises against standard of care and supports practice change.
• ·Expansion cohorts, basket and adaptive designs compress the phases and need careful reading.