@teriabruzzo8 , there is a little more discussion (including my experience with Signatera) in the thread titled "What exactly is NED (no evidence of disease)" of this forum.

It's far from perfect with regard to pancreatic cancer, but a valuable component of a multi-pronged monitoring strategy. My experience (disclaimer: Sample of ONE!) is that CA19-9 was the most significant, most affordable, and most easily tested early sign of my PC recurrence.