progression-free survival

Progression-free survival is the length of time during and after the treatment of a disease, such as cancer, that a patient lives with the disease but it does not get worse. The US National Cancer Institute lists it as one of the standard ways of seeing how well a new treatment works in a clinical trial. It is usually shortened to PFS and reported as a median: the point at which half the group had seen their disease progress and half had not.

It answers a different question from overall survival, which counts only deaths. Progression-free survival counts the disease growing again as well, so it registers a benefit earlier and it captures something patients feel directly, the time before the scan shows the tumour moving. Because it reads out sooner than a survival figure, trials often report it first.

The trade-off is that it depends on when and how the scans were done, so trials that report it well use a blinded independent review of the images rather than leaving the judgement to the treating doctor. A gain in progression-free survival does not automatically mean people live longer, which is why regulators normally want to see it alongside overall survival before treating it as proof of benefit.