PanNETs are classified based on their functional status and grade. Functionally, they can be categorized as insulinomas, gastrinomas, glucagonomas, somatostatinomas, and VIPomas, each associated with a different hormone and clinical syndrome. The World Health Organization (WHO) classifies these tumors into grades 1 to 3 based on mitotic count and Ki-67 index, which is a marker of proliferation. Grade 1 and 2 tumors tend to be slower growing and less aggressive, whereas grade 3 tumors demonstrate more aggressive behavior with a poorer prognosis.
