Stage III includes: IIIA: (T1a, N1, M0); (T1b, N1, M0); (T2, N1, M0); (T3a, N1, M0); (T3b, N1, M0); IIIB: (T4, Any N, M0); (Any T, N2, M0). T1a: Tumor limited to ampulla of Vater or sphincter of Oddi. T1b: Tumor invading beyond the sphincter of Oddi (perisphincteric invasion) and/or into the duodenal submucosa. T2: Tumor invading into the muscularis propria of the duodenum. T3a: Tumor directly invading the pancreas (up to 0.5 cm). T3b: Tumor extending more than 0.5 cm into the pancreas, or extending into peripancreatic tissue or duodenal serosa without involvement of the celiac axis or superior mesenteric artery. T4: Tumor involving the celiac axis, superior mesenteric artery, and/or common hepatic artery, irrespective of size. N1: Metastasis to one to three regional lymph nodes. N2: Metastasis to four or more regional lymph nodes. M0: No distant metastasis. (AJCC 8th ed.) [from NCI]