Clinical trials are set up to look at specific outcomes. In some trials, researchers look at progression-free survival (PFS), a measure of how long someone is on a treatment before their cancer starts to grow. They can also look at overall survival (OS), or how long someone lives after starting on a treatment.
Some researchers and advocates say that PFS can be used as a substitute for OS because results come in sooner. They also argue that PFS matters to patients, even if it doesn’t affect their OS. Other researchers and advocates disagree. They point out that PFS doesn’t always predict OS, and using it could lead patients to think a treatment is more effective than it actually is.
Below you can learn more about how PFS and OS are used to measure treatment effectiveness and what questions to ask about PFS and OS when you are thinking about entering a clinical trial or starting a new treatment.
- AstraZeneca: OS, PFS, and other related terms are defined here
- Cancer Research UK: PFS and OS are two endpoints that can be measured in a clinical trial
- Dana-Farber Cancer Institute (video): Dr. Erica Mayer explains an important limitation of overall survival
- Dr. David Oster (video): OS measures how long someone lives, and progression-free survival measures how long someone survives without the disease getting worse (explanation of PFS vs OS begins at 5:13)
Last Modified on April 30, 2024