Progression-free survival in cancer trials is the time from enrollment until death, new lesion development, a 20% increase in tumor size, or a 20% tumor shrinkage before growth.

“progression-free survival which comes up just so often in cancer it's a unique endpoint it's really often interpreted in the lay press as the time it takes for cancer to get worse that's not quite right so progression-free survival is the time from when a patient enrolls on a study to one of four things really happening to them one they could die the first thing they could be going along and then one day they should they could just die so that's part of the end point so if you die first that's it you have a pfs event fortunately for most trials that's not the most common thing that counts as a pfs invent the second thing that could happen is you have a new lesion on your cat scan we're scanning you along and your lungs we didn't find anything but now there's a little ditzel there and i stick a needle in it and it's pancreas cancer so you have progressed you got a new lesion that's progression the third thing that could happen is your tumor that we measured at one centimeter it got to 1.2 centimeters it got 20 percent bigger the moment it gets 20 percent bigger 21 percent bigger it's progression when it's 19 percent bigger oh it's stable disease that's what we call that that's stable but then 20 21 that's progression so it's an arbitrary cut point very arbitrary and that's why it doesn't always track with how people feel the fourth thing that could happen is your tumor got smaller before it got bigger and if your tumor got smaller before it gets bigger it's 20 from the smallest it ever was”