Multimodal imaging evaluation in staging of rectal cancer

Table 1 Tumor nodes metastasis staging of rectal cancer based on the American Joint Committee on Cancer 7^th edition

Primary tumor (T)
Tx	Primary tumor cannot be assessed
T0	No evidence of primary tumor
Tis	Carcinoma in situ
T1	Tumor invades submucosa
T2	Tumor invades muscularis propria
T3	Tumor invades through the muscularis propria and into perirectal tissues
T4a	Tumor penetrates to the surface of the visceral peritoneum
T4b	Tumor directly invades or is adherent to other organs or structures
Regional lymph nodes (N)
Nx	Regional lymph nodes cannot be assessed
N0	No regional lymph node metastasis
N1	Metastases in 1-3 regional lymph nodes
N1a	Metastasis in 1 regional lymph node
N1b	Metastases in 2-3 regional lymph nodes
N1c	Tumor deposit(s) in the subserosa, mesentery, pericolic, or perirectal tissues without regional nodal metastasis
N2	Metastases in 4 or more regional lymph nodes
N2a	Metastases in 4-6 regional lymph nodes
N2b	Metastases in 7 or more regional lymph nodes
Distant metastasis (M)
M0	No distant metastasis
M1	Distant metastasis
M1a	Metastasis confined to 1 organ or site (e.g., liver, lung, ovary, non-regional node, external iliac lymph node)
M1b	Metastases in > 1 organ/site or the peritoneum

Note-Adapted from the American Joint Committee on Cancer staging system[3].