Table 2. Definitions of American Joint Committee on Cancer (AJCC) staging system for iCCA, pCCA, and dCCA with 8th editions.

	iCCA	pCCA	dCCA
T	Primary Tumor	Primary Tumor	Primary Tumor
TX	Primary tumor cannot be assessed	Primary tumor cannot be assessed	Primary tumor cannot be assessed
T0	No evidence of primary tumor	No evidence of primary tumor	―
Tis	Carcinoma in situ (intraductal tumor)	Carcinoma in situ/high-grade dysplasia
T1	Solitary tumor without vascular invasion, ≤ 5cm or >5 cm	Tumor confined to the bile duct, with extension up to the muscle layer or fibrous tissue	Tumor invades the bile duct wall with a depth less than 5 mm
T1a	Solitary tumor ≤ 5cm without vascular invasion
T1b	Solitary tumor >5 cm without vascular invasion
T2	Solitary tumor with intrahepatic vascular invasion or multiple tumors, with or without vascular invasion
T2a		Tumor invades beyond the wall of the bile duct to surrounding adipose tissue	Tumor invades the bile duct wall with a depth of 5-12 mm
T2b		Tumor invades beyond the wall of the bile duct to surrounding adipose tissue
T3	Tumor perforation of the visceral peritoneum	Tumor invades unilateral branches of the portal vein or hepatic artery	Tumor invades the bile duct wall with a depth greater than 12 mm
T4	Tumor involving local extrahepatic structures by direct invasion	Tumor invades the main portal vein or its branches bilaterally, or the common hepatic artery, or unilateral second order biliary radicals with contralateral portal vein or hepatic artery involvement	Tumor involves the celiac axis, the superior mesenteric artery, and/or common hepatic artery
N	Regional lymph nodes	Regional lymph nodes	Regional lymph nodes
NX	Regional lymph nodes cannot be assessed	Regional lymph nodes cannot be assessed	Regional lymph nodes cannot be assessed
N0	No regional lymph node metastasis	No regional lymph node metastasis	No regional lymph node metastasis
N1	Regional lymph node metastasis present	One to three positive lymph nodes typically involving the hilar, cystic duct, common bile duct, hepatic artery, posterior pancreatoduodenal, and portal vein lymph nodes	Metastasis to one to three regional lymph nodes
N2	―	Four or more positive lymph nodes from the sites described for N1	Metastasis to four or more regional nodes
M	Distant Metastasis	Distant Metastasis	Distant Metastasis
M0	No distant metastasis	No distant metastasis	No distant metastasis
M1	Distant metastasis present	Distant metastasis present	Distant metastasis present