Table 1.
Classification and grading criteria for neuroendocrine neoplasms (NENs) of the gastrointestinal tract and hepatopancreatobiliary organs after the WHO 2019 classification.
| Terminology | Differentiation | Grade | Mitotic Rate (mitoses/2 mm2) | Ki-67 Index |
|---|---|---|---|---|
| NET, G1 | Well differentiated | Low | <2 | <3% |
| NET, G2 | Intermediate | 2–20 | 3–20% | |
| NET, G3 | High | >20 | >20% | |
| NEC, small-cell type | Poorly differentiated | High | >20 | >20% |
| NEC, large-cell | >20 | >20% | ||
| MiNEN | Well or poorly | Variable | Variable | Variable |
NEC: Neuroendocrine carcinoma; MiNEN: mixed neuroendocrine-nonneuroendocrine neoplasms; NET: neuroendocrine tumor; Ki-67 index: rate of cell growth.