Table 1.
Histopathological classification of neuroendocrine tumors.
| Histological classification | Well-differentiated (low grade, G1) | Moderately differentiated (intermediate grade, G2) | Poorly differentiated (high grade, G3) |
|---|---|---|---|
| Appearance | Monomorphic population of small round cells | Undefined | Cellular pleomorphism |
| Prognosis | Prolonged survival | Intermediate | Poor |
| Mitotic rate* | <2 | 2–20 | >20 |
| Ki-67 index** | <3% | 3–20% | >20% |
| Necrosis | Absent | Undefined | Present |
*Per 2 mm2; **percentage of tumor cells that immunolabel positively for Ki-67 antigen.