I would ask the docs who are about to perform your EUS on Wednesday if they can extract enough tissue to send out for a full genetic workup, not just a diagnosis of malignant cells or not.

It can be helpful if there is enough tissue available for outside analysis, and maybe send slides to Mayo in advance of your consult with them.

I don't know if they can get enough tissue via FNA to also build the Signatera test for you. Signatera does a genetic analysis of your tumor tissue, and then builds a special blood test that looks for exactly the same DNA in your bloodstream later on during treatment. It can be a very helpful complement to imaging and CA19-9 monitoring.

It's also possible for the EUS to miss malignant tissue. When my tumor came back at the original (Whipple) surgery site, it was 1.3 cm already. The surgeon took four samples during EUS, and had two pathologists/surgeons examine them all. He was absolutely positive if cancer was there, he would have gotten a piece of it. They found no malignant cells and concluded it was a case of pancreatitis, but imaging, CA19-9, and Signatera 6 weeks later confirmed a true recurrence of PDAC.

Another surgeon told me the post-Whipple anatomy may have made the EUS access a bit more difficult. My suspicion is that since my tumor recurrence started on the outside of the "junction" (anastomosis) where they attached the remaining pancreas to my jejunum, and the endoscopy approached this from the inside, they just couldn't dig deep enough into the wall to find it.

So, even the EUS/FNA is not perfect. There are other tests (e.g., from Guardant) that can detect circulating tumor DNA at microscopic levels. You should inquire about having one of those, as well as a germline DNA test (like Invitae) for inherited mutations. Both of these take several weeks to get results, but you would have those in the pipeline, and the answers might help guide your treatment when (if) the time comes.

I don't know how to speed things up at the Mayo. I'm impressed you've even got a callback scheduled without a definitive diagnosis going in.

Wishing you all the best!