Table 1.

American Joint Committee on Cancer (AJCC) staging system by tumor–node–metastasis (TNM) stage on imaging

Stage	AJCC, 7th edition	AJCC, 8th edition
Tumor (T) stage
T1	Tumor confined to the bile duct, with extension up to the muscle layer or fibrous tissue
T2a	Tumor invades beyond the wall of the bile duct to surrounding adipose tissue
T2b	Tumor invades adjacent hepatic parenchyma
T3	Tumor invades unilateral branches of the PV or HA
T4	Tumor invades main PV or its branches bilaterally, or the common hepatic artery, second-order bile ducts bilaterally, unilateral second-order bile ducts with contralateral portal vein or hepatic artery involvement	Tumor invades main PV or its branches bilaterally, or the common hepatic artery, or unilateral second-order biliary radicals with contralateral portal vein or hepatic artery involvement.
Node (N) stage
N0	No regional lymph node metastasis	No regional lymph node metastasis
N1	Regional lymph node metastasis: hilar (along CBD, cystic duct, HA, or PV)	One to three positive lymph nodes typically involving the hilar, cystic duct, common bile duct, hepatic artery, posterior pancreatoduodenal, and portal vein lymph nodes
N2	Metastasis to periaortic, pericaval, SMA, or coeliac lymph nodes	Four or more positive lymph nodes from the sites described for N1
Metastasis (M) stage
M0	No distant metastasis	No distant metastasis
M1	Distant metastasis	Distant metastasis (includes lymph node metastasis distant to the hepatoduodenal ligament)