Examples of well-differentiated neuroendocrine tumors (NETs) of the digestive organs

(A) EC (enterochromaffin) cell NET (carcinoid) of the terminal ileum shows solid tumor nest with peritumoral fibrosis.
(B) Pancreatic NET with ribbon-like pattern and wide tumor-free spaces in between.
(C) Pancreatic insulinoma shows abundant amyloid deposition.
(D) Periampullary somatostatinoma shows tubuloglandular pattern with numerous psamomma bodies. (H&E, 400x original magnification.)