T — primary tumour
Tis — intramucosal carcinoma (no invasion through the muscularis mucosae)
T1 — invades the submucosa
T2 — invades the muscularis propria
T3 — through the muscularis propria into pericolorectal tissues
T4a — penetrates the visceral peritoneum
T4b — directly invades or is adherent to adjacent organs or structures
N — regional lymph nodes
N0 — no regional lymph node metastasis
N1a — metastasis in 1 regional lymph node
N1b — metastasis in 2–3 regional lymph nodes
N1c — tumour deposit(s) in the subserosa or mesentery, no positive nodes
N2a — metastasis in 4–6 regional lymph nodes
N2b — metastasis in ≥ 7 regional lymph nodes
M — distant metastasis
M0 — no distant metastasis
M1a — metastasis to one site or organ, no peritoneal involvement
M1b — metastasis to ≥ 2 sites or organs, no peritoneal involvement
M1c — peritoneal metastasis, with or without other organ involvement
Evidence
Original publication
Weiser MR. AJCC 8th Edition: Colorectal Cancer. Reviews the 8th-edition refinements — tumour deposits (N1c), sub-stratification of stage III by T and N, and M1a/M1b/M1c by number of involved sites and peritoneal involvement.
Annals of Surgical Oncology, 2018
Guideline
Amin MB, Edge SB, Greene FL, et al., eds. AJCC Cancer Staging Manual, 8th edition. Chicago: Springer; 2017. Confirm the assigned stage against the manual, particularly the dense stage III sub-groups.
Last reviewed: 2026-09
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MedScore is an educational and clinical decision-support tool. It does not provide a diagnosis, a treatment, or a drug-dosing recommendation, and it does not replace clinical judgement or local guidelines. Confirm every result against the original source before acting on it. The treating clinician remains responsible for all decisions.