Stage II includes: IIA: T3, N0, M0; IIB: T4, N0, M0. T3: Tumor invading through the muscularis propria into the subserosa, or extending into nonperitonealized perimuscular tissue (mesentery or retroperitoneum) without serosal penetration. 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. T4: Tumor perforating the visceral peritoneum or directly invading other organs or structures (e.g., 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). N0: No regional lymph node metastasis. M0: No distant metastasis. (AJCC 8th ed.) [from NCI]