Hello @casualsuman. I'd like to join @colleenyoung in welcoming you to Connect. I've had surgeries for three neuroendocrine tumors (NETs) in the upper digestive tract and Chromogranin A is one of several diagnostic tests used when doctors suspect a diagnosis of NETs. Here is an explanation from the Carcinoid Cancer Foundation regarding diagnostic tests:
--Diagnosis and Follow-Up Tests.
https://www.carcinoid.org/for-patients/diagnosis/diagnosis-and-follow-up-tests/
When there is a high CgA combined with other markers, a diagnosis of NETs is suspected. Have your dad's doctors said that his tumor was a NET? (This would show up in the biopsy report.)