TNM classification for small bowel adenocarcinoma

Tx: Primary tumor cannot be assessed

T0: No evidence of primary tumor

Tis: High-grade dysplasia/carcinoma in situ

T1a: Tumor invades lamina propria

T1b: Tumor invades submucosa

T2: Tumor invades muscularis propria

T3: Tumor invades through muscularis propria into subserosa or extends into nonperitonealized perimuscular tissue (mesentery or retroperitoneum) without serosal penetration

T4: Tumor perforates visceral peritoneum or directly invades other organs or structures (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)