Colon Cancer Staging

Updated: Feb 05, 2021
Author: Shamudheen Rafiyath, MD; Chief Editor: N Joseph Espat, MD, MS, FACS 

TNM Classification for Colon Cancer

Colon cancer is staged using the American Joint Committee on Cancer (AJCC) tumor/node/metastasis (TNM) classification and staging system. In this system, stages are assigned on the basis of the characteristics of the primary tumor (T) and the extent of regional lymph node involvement (N) and distant metastasis (M). In addition, metastasis may be defined clinically or pathologically, on the basis of preoperative clinical assessment (c) or pathologic evaluation of metastatic tissue (p).[1, 2]  

 

Table 1. TNM Classification for Colon Cancer (Open Table in a new window)

Primary tumor (T)

TX

Primary tumor cannot be assessed

T0

No evidence of primary tumor

Tis

Carcinoma in situ: intraepithelial or intramucosal carcinoma (involvement of lamina propria with no extension through the muscularis mucosa)

T1

Tumor invades submucosa (through the muscularis mucosa but not into the muscularis propria)

T2

Tumor invades muscularis propria

T3

Tumor invades through the muscularis propria into the pericolorectal tissues

T4

Tumor invades the visceral peritoneum or invades or adheres to adjacent organ or structure

T4a

Tumor invades through the visceral peritoneum (including gross perforation of the bowel through tumor and continuous invasion of tumor through areas of inflammation to the surface of the visceral peritoneum)

T4b

Tumor directly invades or is adherent to other organs or structures
T Suffix Definition
(m) Select if synchronous primary tumors are found in a single organ

Definition of regional lymph nodes (N)

NX

Regional lymph nodes cannot be assessed

N0

No regional lymph node metastasis

N1

Metastasis in 1-3 regional lymph nodes (tumor in lymph nodes measuring ≥0.2 mm) or any number of tumor deposits are present and all identifiable nodes are negative

N1a

Metastasis in 1 regional lymph node

N1b

Metastasis in 2-3 regional lymph nodes

N1c

Tumor deposit(s) in the subserosa, mesentery, or nonperitonealized, pericolic, or perirectal/mesorectal tissues without regional nodal metastasis

N2

Metastasis in 4 or more lymph nodes

N2a

Metastasis in 4-6 regional lymph nodes

N2b

Metastasis in 7 or more regional lymph nodes
N Suffix Definition
(sn) Select if regional lymph node metastasis identified by sentinel lymph node biopsy only
(f) Select if regional lymph node metastasis identified by fine needle aspiration or core needle biopsy

Definition of distant metastasis (M)

The terms pM0 and Mx are not valid categories in the TNM system. Assignment of the M category for clinical classification may be cM0, cM1 or pM1. Any of the categories (cM0, CM1 or pM1) may be used with pathological stage grouping.
MCategory M Criteria

cM0

No distant metastasis by imaging or other studies, no evidence of tumor in distant sites or organs. (This category is not assigned by pathologists.)

cM1

Metastasis to one or more distant sites or organs or peritoneal metastasis is identified

cM1a

Metastasis confined to 1 organ or site is identified without peritoneal metastasis

cM1b

Metastasis to two or more sites or organs is identified without peritoneal metastasis

M1c

Metastasis to the peritoneal surface alone or with other site or organ metastases
pM1 Metastasis to one or more distant sites or organs or peritoneal metastasis is identified and microscopically confirmed
pM1a Metastasis to one site or organ is identified without peritoneal metastasis and microscopically confirmed
pM1b Metastasis to two or more sites or organs is identified without peritoneal metastasis and microscopically confirmed.
pM1c Metastasis to the peritoneal surface is identified alone or with other site or organ metastasis and microscopically confirmed

Table 2. Anatomic stage/prognostic groups (Open Table in a new window)

0

Tis

N0

M0

I

T1

N0

M0

 

T2

N0

M0

IIA

T3

N0

M0

IIB

T4a

N0

M0

IIC

T4b

N0

M0

IIIA

T1-T2

N1/N1c

M0

 

T1

N2a

M0

IIIB

T3-T4a

N1/N1c

M0

 

T2-T3

N2a

M0

 

T1-T2

N2b

M0

IIIC

T4a

N2a

M0

 

T3-T4a

N2b

M0

 

T4b

N1-N2

M0

IVA

Any T

Any N

M1a

IVB

IVC

Any T

Any T

Any N

Any T

M1b

M1c

Staging information

Compared with the 7th edition of the AJCC staging manual, features of revised staging in the 8th edition give more importance to the poor prognostic features of the depth of invasion in spite of fewer positive nodes.

  • T4 is divided between penetration to the surface of visceral peritoneum and direct gross adherence to adjacent structures

  • T1-2N2 is downstaged from stage IIIC to IIIA or IIIB, depending on the number of nodes involved

  • Shift T4bN1 from IIIB to IIIC

  • Subdivide T4/N1/N2

  • Resolution of staging for the issue of mesenteric deposits where nodal tissue is not identified

  • Revised substaging of stage II based on depth of invasion, with the addition of stage IIC

  • Revised substaging of stage III based on node number (N1a—1 node; N1b—2-3 nodes; N2a—4-6 nodes; N2b—7 or more nodes)

  • Division of metastases to 1 or more sites in recognition of the possibility of cure with aggressive treatment of single site of metastatic disease

  • Stage M1c has been introduced to represent the poor prognosis of peritoneal carcinomatosis.

  • Nodal micrometastases (tumor clusters ≥0.2 mm in diameter) are now scored as positive due to results of meta-analysis demonstrating poor prognosis in these patients.[3]

  • Other tumor deposits in the peritoneum, subserosa, and mesentery are given equal weight as nodal metastases.

The following factors are important in determining treatment decisions but are not yet incorporated into the formal staging criteria:

  • Preoperative serum carcinoembryonic antigen (CEA) levels

  • Tumor regression score reflective of the pathologic response to preoperative chemotherapy, chemoradiotherapy, radiotherapy, or chemobiologic therapy as well as the status of circumferential margin for rectal cancer.

  • Lymphovascular and perineural invasion

  • Microsatellite instability (MSI), which represents deficiency of mismatch repair enzymes and is both a prognostic factor and predictive of lack of response to fluoropyrimidine therapy in the adjuvant setting.

  • Mutation status of KRAS, NRAS, and BRAF, because mutations in those genes are associated with lack of response to agents targeting epidermal growth factor receptors.  

 

Questions & Answers

Overview

How is colon cancer staged?