Table I.

TNM classification (version 5, 1997) with subclassifications.

TNM	Stage	Extension to
Tis N0 M0	0	Carcinoma in situ: intraepithelial or invasion of lamina propria
T1 N0 M0	I	Submucosa
T2 N0 M0	I	Muscularis propria
T3 N0 M0	IIA	Subserosa/perirectal tissue
	Substaginga	T3a	Less than 1 mm
		T3b	1–5 mm
		T3c	5–15 mm
		T3d	15 + mm
T4 N0 M0	IIB	(b) Perforation into visceral peritoneum; or (a) invasion to other organsb
T1–2 N1 M0	IIIA	1–3 regional nodes involved
T3–4 N1 M0	IIIB	1–3 regional nodes involvedc
T1–4 N2 M0	IIIC	4 or more regional nodes involved
T1–4 N1–2 M1	IV	Distant metastases

^aThis subclassification based upon an evaluation using MRI prior to treatment decision is clinically valuable, and used when describing the treatment strategy for primary rectal cancer. It can be used also in the histopathological classification but is not yet validated and therefore not incorporated in any of the TNM versions 5–7.

^bThis is the subclassification in TNM 5. It has been reversed in TNM 6 and 7.

^cLymph node classification is modified in TNM 7. Tumour cell deposits without a visible lymph node structure are also considered. It is recommended to investigate at least 12 nodes for proper staging.