Progression-free survival (PFS) measures the effect of a drug on a disease, usually cancer. There is no single definition of PFS, but it usually measures progression by growth of the tumor, new tumors, death from the cancer, or death from other causes. Progression-free survival is in contrast to overall survival (OS), which measures whether the patients treated with a drug live longer than patients who are not treated with the drug. PFS accurately predicts OS for some cancers, but not for others. OS is generally considered a more meaningful endpoint than PFS, since OS measures actual survival. A drug can extend PFS, but not OS.
The advantage of measuring PFS over measuring OS (that is, deaths) is that PFS appears sooner than deaths, allowing faster trials, and appears more frequently than deaths, allowing smaller trials. Oncologists feel that PFS can give them a better idea of how the cancer is progressing during the course of treatment, rather than waiting for the patients' deaths to evaluate the drug.
The disadvantage of measuring PFS is that many drugs improve PFS without improving survival, or even quality of life.
Traditionally, the U.S. Food and Drug Administration has required studies of OS rather than PFS to demonstrate that a drug is effective against cancer, but recently the F.D.A. has accepted PFS. The use of PFS for proof of effectiveness and regulatory approval is controversial.
It is a metric frequently used by the UK National Institute for Health and Clinical Excellence and the U.S. Food and Drug Administration to evaluate the effectiveness of a cancer treatment. PFS has been postulated to be a better ("more pure") measure of efficacy in second-line clinical trials as it eliminates potential differential bias from prior or subsequent treatments.
However, PFS improvements do not always result in corresponding improvements in overall survival, and the control of the disease may come at the biological expense of side effects from the treatment itself. This has been described as an example of the McNamara fallacy.
Time to progression
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- BMJ 31-Jan-2009 "NICE and the challenge of cancer drugs" p271
- Booth, Christopher M.; Eisenhauer, Elizabeth A. (2012). "Progression-Free Survival: Meaningful or Simply Measurable?". Journal of Clinical Oncology 30 (10): 1030–1033. doi:10.1200/JCO.2011.38.7571.
- "Progression-free survival and time to progression as primary end points in advanced breast cancer: often used, sometimes loosely defined".
- "Guidance for Industry Clinical Trial Endpoints for the Approval of Cancer Drugs and Biologics".
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