William,
I wish you and your son the best of strength. You will win this!
Sorry I only know about Paraganglioma (PG) and Pheochromocytoma (PH) NEC tumors.
Blood tests are an important part like all say here.
There are two other very important things to consider.
Active PH and PGs secret fight-and-flight hormones like adrenaline, dopamine, norepinephrine. This means very high blood pressure episodes, sleeping problems, and such. Have you noticed anything like that?
Second thing is genetic testing for NECs. It can be a blood test or a saliva swab.
They are looking for mutations in succinate dehydrogenase enzyme complex or SDH. We all get two of each SDH genes, one from each parent. SDHA, SDHB, SDHC, SDHD, and SDHAF2. They are as rare as NEC tumors. If you the SDH mutation, there is a 40%+ chance for PH or PG. If you have the mutation, there s a 50/50 chance it is passed to the kids. If they don't have it, mutation will die with you. Only SDHB mutation can be passed by father or mother. It is the most aggressive buggar I have been told when I got tested positive for it. All other SDH mutations can be passed by the father only.
MD Anderson did not do a genetic test till after I was diagnosed with Carotid Body PG (paraganglioma). I had renal cysts that did not show up on the Dotatate PetCT scan, no Pheochromocytoma thankfully. With the mutation I am to be retested every six month or a year depending on possible symptoms.
He's up, results for the NEC genetic mutation tests take a couple of weeks or more to get back.
Stay strong! Hope information helps.