| Primary tumor (T) | |||
| T category | T criteria | ||
| TX | Primary tumor cannot be assessed | ||
| T0 | No evidence of primary tumor | ||
| Tis | High-grade dysplasia/carcinoma in situ | ||
| T1 | Tumor invades the lamina propria or submucosa | ||
| T1a | Tumor invades the lamina propria | ||
| T1b | Tumor invades the submucosa | ||
| T2 | Tumor invades the muscularis propria | ||
| T3 | Tumor invades through the muscularis propria into the subserosa, or extends into nonperitonealized perimuscular tissue (mesentery or retroperitoneum) without serosal penetration* | ||
| T4 | Tumor perforates the visceral peritoneum or directly invades other organs or structures (eg, other loops of small intestine, mesentery of adjacent loops of bowel, and abdominal wall by way of serosa; for duodenum only, invasion of pancreas or bile duct) | ||
| * For T3 tumors, the nonperitonealized perimuscular tissue is, for the jejunum and ileum, part of the mesentery and, for the duodenum in areas where serosa is lacking, part of the interface with the pancreas. | |||
| Regional lymph nodes (N) | |||
| N category | N criteria | ||
| NX | Regional lymph nodes cannot be assessed | ||
| N0 | No regional lymph node metastasis | ||
| N1 | Metastasis in one or two regional lymph nodes | ||
| N2 | Metastasis in three or more regional lymph nodes | ||
| Distant metastasis (M) | |||
| M category | M criteria | ||
| M0 | No distant metastasis | ||
| M1 | Distant metastasis present | ||
| Prognostic stage groups | |||
| Adenocarcinoma | |||
| When T is... | And N is... | And M is... | Then the stage group is... |
| Tis | N0 | M0 | 0 |
| T1-2 | N0 | M0 | I |
| T3 | N0 | M0 | IIA |
| T4 | N0 | M0 | IIB |
| Any T | N1 | M0 | IIIA |
| Any T | N2 | M0 | IIIB |
| Any T | Any N | M1 | IV |
