COLON AND RECTUM (ICD‐O‐3 C18–20)

Rules for Classification

The classification applies only to carcinomas. There should be histological confirmation of the disease.

Anatomical Sites and Subsites

Colon (C18) (Fig. 170)

Caecum (C18.0)
Ascending colon (C18.2)
Hepatic flexure (C18.3)
Transverse colon (C18.4)
Splenic flexure (C18.5)
Descending colon (C18.6)
Sigmoid colon (C18.7)

Rectosigmoid junction (C19) (Fig. 171)

Rectum (C20) (Fig. 171)

Schematic illustration of the details of colon. — **Fig. 170**

Schematic illustration of Rectosigmoid junction. — **Fig. 171**

Regional Lymph Nodes

For each anatomical site or subsite, the following are regional lymph nodes:

Caecum	Ileocolic, right colic (Fig. 172)
Ascending colon	Ileocolic, right colic, middle colic (Fig. 173)
Hepatic flexure	Middle colic, right colic (Fig. 174)
Transverse colon	Right colic, middle colic, left colic, inferior mesenteric (Fig. 175)

Splenic flexure Descending colon Sigmoid colon	Middle colic, left colic, inferior mesenteric (Fig. 176) Left colic, inferior mesenteric (Fig. 177) Sigmoid, left colic, superior rectal (haemorrhoidal), inferior mesenteric and rectosigmoid (Fig. 178)
Rectum	Superior, middle, and inferior rectal (haemorrhoidal), inferior mesenteric, internal iliac, mesorectal (paraproctal), lateral sacral, presacral, sacral promontory (Gerota) (Fig. 179)

Schematic illustration of Ileocolic, right colic. — **Fig. 172**

Schematic illustration of Ileocolic, right colic, middle colic. — **Fig. 173**

Schematic illustration of Middle colic, right colic. — **Fig. 174**

Schematic illustration of Right colic, middle colic, left colic, inferior mesenteric. — **Fig. 175**

Schematic illustration of Middle colic, left colic, inferior mesenteric. — **Fig. 176**

Schematic illustration of Left colic, inferior mesenteric. — **Fig. 177**

Schematic illustration of Sigmoid, left colic, superior rectal, inferior
mesenteric and rectosigmoid. — **Fig. 178**

Schematic illustration of Superior, middle, and inferior rectal (haemorrhoidal), inferior
mesenteric, internal iliac, mesorectal (paraproctal), lateral sacral, presacral, sacral promontory. — **Fig. 179**

Metastasis in nodes other than those listed above is classified as distant metastasis.

TNM Clinical Classification

T – Primary Tumour

TX	Primary tumour cannot be assessed
T0	No evidence of primary tumour
Tis	Carcinoma in situ: intraepithelial or invasion of lamina propria¹
T1	Tumour invades submucosa (Fig. 180)
T2	Tumour invades muscularis propria (Fig. 181)
T3	Tumour invades subserosa or into non‐peritonealized pericolic or perirectal tissues (Fig. 182)
T4	Tumour directly invades other organs or structures^2,^3,⁴ and/or perforates visceral peritoneum (Figs. 183, 184)
T4a	Tumour perforates visceral peritoneum
T4b	Tumour directly invades other organs or structures

Notes

¹ Tis includes cancer cells confined within mucosal lamina propria (intramucosal) with no extension through the muscularis mucosae into the submucosa.

² Invades through to visceral peritoneum to involve the surface.

³ Direct invasion in T4b includes invasion of other organs or segments of the colorectum by way of the serosa, as confirmed on microscopic examination, or for tumours in a retroperitoneal or subperitoneal location, direct invasion of other organs or structures by virtue of extension beyond the muscularis propria.

⁴ Tumour that is adherent to other organs or structures, macroscopically, is classified as cT4b. However, if no tumour is present in the adhesion, microscopically, the classification should be pT1–3, depending on the anatomical depth of wall invasion.

Schematic illustration of tumour invades submucosa. — **Fig. 180**

Schematic illustration of tumour invades muscularis propria. — **Fig. 181**

Schematic illustration of tumour invades subserosa or into non‐peritonealized pericolic or perirectal tissues. — **Fig. 182**

Schematic illustration of tumour directly invades other organs or structures 2,3,4 and perforates visceral peritoneum. — **Fig. 183**

N – Regional Lymph Nodes

NX	Regional lymph nodes cannot be assessed
N0	No regional lymph node metastasis
N1	Metastasis in 1 to 3 regional lymph nodes (Fig. 185)
	N1a	Metastasis in 1 regional lymph node
	N1b	Metastasis in 2 to 3 regional lymph nodes
	N1c	Tumour deposit(s), i. e. satellites^, in the subserosa, or in non‐peritonealized pericolic or perirectal soft tissue without* regional lymph node metastasis
N2	Metastasis in 4 or more regional lymph nodes (Figs. 186, 187, 188)
	N2a	Metastasis in 4 to 6 regional lymph nodes
	N2b	Metastasis in 7 or more regional lymph nodes

Schematic illustration of Metastasis in 1 to 3 regional lymph nodes. — **Fig. 185**

Schematic illustration of Metastasis in 4 or more regional lymph nodes. — **Fig. 186**

Schematic illustration of Metastasis in 4 to 6 regional lymph nodes. — **Fig. 187**

Schematic illustration of Metastasis in 7 or more regional lymph nodes. — **Fig. 188**

Note

^* Tumour deposits (satellites) are discrete macroscopic or microscopic nodules of cancer in the pericolorectal adipose tissue’s lymph drainage area of a primary carcinoma that are discontinuous from the primary and without histological evidence of residual lymph node or identifiable vascular or neural structures. If a vessel wall is identifiable on H&E, elastic or other stains, it should be classified as venous invasion (V1/2) or lymphatic invasion (L1). Similarly, if neural structures are identifiable, the lesion should be classified as perineural invasion (Pn1). The presence of tumour deposits does not change the primary tumour T category, but changes the node status (N) to pN1c if all regional lymph nodes are negative on pathological examination.

M – Distant Metastasis

M0	No distant metastasis
M1	Distant metastasis
	M1a	Metastasis confined to one organ (liver, lung, ovary, non‐regional lymph node(s)), without metastases to the peritoneum
	M1b	Metastases in more than one organ without metastases to the peritoneum
	M1c To peritoneum with or without other organs

TNM Pathological Classification

The pT and pN categories correspond to the T and N categories.

pM1	Distant metastasis microscopically confirmed

Note

pM0 and pMX are not valid categories.

pN0

Histological examination of a regional lymphadenectomy specimen will ordinarily include 12 or more lymph nodes. If the lymph nodes are negative, but the number ordinarily examined is not met, classify as pN0.