PNETs are classified based on their ability to secrete hormones. Functional PNETs produce hormones that cause distinct clinical syndromes (e.g., insulinomas, gastrinomas). Non-functional PNETs do not secrete hormones and may be asymptomatic until they grow large or metastasize. Pathologically, PNETs are also graded based on their cell differentiation and proliferation rate.
