| T: primary tumor | |
| TX | Primary tumor cannot be assessed |
| T0 | No evidence of primary tumor |
| T1 | Tumor invades lamina propria or submucosa and is 1 cm or less in greatest dimension |
| T2 | Tumor invades muscularis propria or is more than 1 cm in greatest dimension |
| T3 | Tumor invades subserosa (gastric NET) or pancreas / peripancreatic adipose tissue (duodenal NET) |
| T4 | Tumor perforates serosa or invades other adjacent structures |
| N: regional lymph nodes | |
| NX | Regional lymph nodes cannot be assessed |
| N0 | No regional lymph node metastasis |
| N1 | Regional lymph node metastasis |
| M: distant metastasis | |
| M0 | No distant metastasis |
| M1a | Hepatic metastasis only |
| M1b | Extrahepatic metastasis only |
| M1c | Hepatic and extrahepatic metastases |
