I don't really agree with one thing here: it's difficulty to diagnose. Most Interventional radiologists or endo docs are able to hit pancreatic lesions with ease, even sub-centimeter in size. Getting diagnostic tissue/cells isn't "difficult" in the sense that they can't do it, it's more that catching it early is the difficult part of the lesion is really small i.e. early stage typically.

Source: I worked as a cytotech for years dx these tumors. Sure there's differentials in cytology and histology, but any pathologist worth their weight will order special stains to confirm/rule out things that may be "trickier" to look at.