Table 3. TNM classification for appendiceal NETs 20 .
| Tx | Primary tumor cannot be assessed |
| T0 | No evidence of primary tumor |
| T1 | ≤ 2 cm in greatest dimension |
| T2 | Between 2 and 4 cm in greatest dimension |
| T3 | > 4 cm or with subserosal invasion or involvement of the mesoappendix |
| T4 | Tumor perforated the peritoneum or directly invades other adjacent organs or structures (excluding direct mural extension to adjacent subserosa of adjacent bowel), e.g., abdominal wall and skeletal muscle |
| Nx | Regional lymph nodes cannot be assessed |
| N0 | No regional lymph node metastasis |
| N1 | Regional lymph node metastasis |
| M0 | No distant metastasis |
| M1 | Distant metastasis |
| M1a | Metastasis confirmed to the liver |
| M1b | Metastases in at least one extrahepatic site |
| M1c | Both hepatic and extrahepatic metastases |
Abbreviation: NETs, neuroendocrine tumors.