When you browse our clinical trials radar, each listing shows a Phase I, II or III label. This is not technical detail for doctors — it helps you understand how far along a treatment is in development and what you might expect.
This article explains each phase in simple terms. It is for information only — always discuss a specific trial with your oncologist.
Why does the trial phase matter?
Every new drug or treatment regimen goes through stages of testing in people. The higher the phase:
- more patients have already taken part (in that trial or similar studies of the drug),
- more is known about safety and typical side effects,
- closer we are to confirming whether the treatment actually helps.
That does not mean Phase I is “worse” and Phase III is “better” — it reflects a different stage of knowledge and often a different group of patients the trial is designed for.
Phase I
First tests in humans
What it involves: The drug is tested in people after laboratory studies. Usually a small group of participants takes part.
What the trial checks:
- whether the drug is safe for humans,
- what dose is tolerated,
- what early side effects may occur.
Who it is often for: Sometimes patients who have run out of standard treatment options — but this depends on the specific protocol. Eligibility criteria are usually very strict.
What to watch for: Phase I provides the least information about whether the drug effectively treats cancer — it focuses mainly on safety. Talk carefully with your doctor about the balance of potential benefit and risk.
Phase II
Does the treatment work?
What it involves: The drug is given to a larger group of patients with a particular type of cancer.
What the trial checks:
- whether the drug shows anti-cancer activity,
- what the preliminary effectiveness profile looks like,
- which side effects occur more often.
Who it is often for: Patients with a specific cancer type, often after some prior therapies — but every trial has its own inclusion and exclusion criteria.
What to watch for: Phase II gives the first serious signals about effectiveness, but results are not yet final. Many Phase II trials are still ongoing and interim results need cautious interpretation.
Phase III
Comparison with the best available treatment
What it involves: The drug (or new regimen) is compared with standard treatment in hundreds or thousands of patients, often at many centres worldwide. In oncology, such a comparison almost never means some patients go without treatment — the comparison group usually receives standard, proven therapy.
What the trial checks:
- whether the new treatment is better, worse or similar to the current standard,
- the safety profile in a large population,
- impact on survival time or disease control.
Who it is often for: A broader group of patients who meet the protocol criteria — sometimes earlier-stage, sometimes metastatic, depending on the trial.
What to watch for: Phase III is usually the last major step before applying for routine approval. If a Phase III trial shows good results, the drug may become a new standard option — but that process can take months or years.
Phase IV
After the drug is on the market
What it involves: The drug is already approved and available, but is still monitored in a large population.
What the trial checks:
- long-term side effects,
- effectiveness in everyday practice (outside a tightly controlled research protocol),
- comparisons with other therapies in real-world use.
Who it is for: Patients already using an approved drug — sometimes within observational registries.
Early Phase I
Very early testing, usually with microdoses
Early Phase I (sometimes called Phase 0) comes before classic Phase I. A very small group takes part, and the drug is given at doses much lower than therapeutic levels. The main goal is to see how the body handles the drug — absorption, processing and elimination — not to treat the disease.
What to watch for: Because doses are very low, this stage is not designed to provide a treatment benefit. If you are considering taking part, discuss very carefully with your doctor what you can realistically expect.
Combined phases (e.g. I/II)
You may see Phase I/II or Phase II/III. That means the trial covers goals typical of both phases at once — for example studying dose and early effectiveness together. This is common in modern oncology trials.
How to use this on the radar
On the clinical trials radar, each trial has a ? icon next to the phase — a quick reminder of what that phase means without leaving the list.
When choosing a trial, check with your oncologist:
- Phase — how far along the treatment is,
- Status — whether the trial is actively recruiting,
- Eligibility — whether your case fits the protocol,
- Location — whether you can take part in Poland or abroad.
Important note
Trial phase is only one part of the decision. Two trials in the same phase can differ greatly — different drug, different criteria, different risk.
This article is not medical advice. Always discuss joining a clinical trial with your treating physician, who knows your treatment history.