Initially my surgeon also thought mine was non functional NET in the head of the pancreas and after I informed that I had frequent diarrhoea, did he send me for biopsy. It was diagnosed as functional gastrinoma NET. Whipple surgery in May 2020 to remove the well defined Grade 1, Stage 1 tumor. I still have frequent diarrhoea, occasional heart burnt and CGA is 600+.
It’s indeed frustrating. Hope this information helps.