In simple terms
Progression-free survival, usually shortened to PFS, is a way of measuring whether a treatment is working in a clinical trial.
It counts the time from the moment a patient is randomly assigned to a treatment group until the disease objectively worsens or the patient dies, whichever happens first.
How it works
The US Food and Drug Administration defines PFS as the time from randomization until objective tumor progression or death, whichever occurs first. The European Medicines Agency uses the same construction.
Progression is not judged by how a patient feels. It is recorded from scans and measurements taken on a fixed schedule, so the recorded date depends on when those assessments fall.
That scheduling matters more than it sounds. The EMA warns that uneven assessment intervals between trial arms can introduce detection bias, and that patients who leave a study before progression is documented create censoring that may distort the result.
Regulators treat PFS differently from overall survival, which is the time from randomization until death from any cause. PFS can be read earlier and with fewer patients, and the FDA says it may support traditional or accelerated approval depending on the disease, the size of the effect and the available therapy.
Why it matters
PFS is the reason a drug can reach patients years before anyone knows whether it helps them live longer. It shortens trials and lowers their cost.
It also shapes headlines. A reported gain in months of progression-free survival is not a gain in lifespan. The EMA expects a large PFS effect to show up in overall survival, and says a rational explanation is needed when it does not.
Where you will see it
- Cancer drug approval announcements from the FDA and the European Medicines Agency.
- Results presented at oncology conferences and published in medical journals.
- Trial listings naming PFS as a primary or secondary endpoint.
- Company statements to investors about late-stage trial readouts.
Example
A trial might report median progression-free survival of 11 months on a new combination against 6 months on the comparison treatment, while overall survival data remain immature.
Often confused with
Overall survival counts only deaths, from any cause. Time to progression counts only disease progression and excludes deaths. PFS combines both.
Key facts
- The FDA defines progression-free survival as the time from randomization until objective tumor progression or death, whichever occurs first.1
- Overall survival is the time from randomization until death from any cause; time to progression excludes deaths.1
- The FDA lists earlier readout and smaller sample sizes among the advantages of PFS, and assessment bias in open-label trials among its disadvantages.1
- The EMA defines PFS the same way and warns that unequal assessment intervals between trial arms can cause detection bias.2
- The EMA states that a large PFS effect is generally expected to be associated with an effect on overall survival, and that a rational explanation should be provided when it is not.2
This entry explains a medical term. It is not medical advice. If you are concerned about your health, speak with a qualified health professional.
Related concepts
In the news
Quick checkDoes longer progression-free survival mean patients live longer?Show answer
Not necessarily. PFS measures time until the disease worsens or the patient dies. Overall survival is a separate measure, and a treatment can move one without moving the other.
Sources
- US Food and Drug Administration. Clinical Trial Endpoints for the Approval of Cancer Drugs and Biologics, guidance for industry. Undated (accessed 23 September 2026)
- European Medicines Agency. Appendix 1 to the guideline on the evaluation of anticancer medicinal products in man: methodological consideration for using progression-free survival or disease-free survival in confirmatory trials. Undated (accessed 23 September 2026)
Editorially reviewed by Specialty Digest Editorial TeamLast reviewed September 23, 2026Researched and drafted with AI assistanceReport an issue