Colon tumor
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TNM staging of colorectal carcinoma (AJCC 8th edition)

Author: Elliot Weisenberg, M.D. (see Authors page)

Revised: 12 December 2017, last major update November 2017

Copyright: (c) 2017, PathologyOutlines.com, Inc.

PubMed Search: Colorectal cancer staging[TIAB]

See also: Staging - AJCC 7th edition
Cite this page: Weisenberg, E. TNM staging of colorectal carcinoma (AJCC 8th edition). PathologyOutlines.com website. http://pathologyoutlines.com/topic/colontumorstaging8ed.html. Accessed December 15th, 2017.
Definition / general
  • Adenocarcinoma, high grade neuroendocrine carcinoma and squamous carcinoma of the colon and rectum are covered by this staging system
  • Not covered by this staging system are appendiceal carcinoma, anal carcinoma and well differentiated neuroendocrine tumor (carcinoid)
Essential features
  • AJCC 7th edition will sunset on December 31, 2017
  • As of January 1, 2018, use of the 8th edition will be mandatory, although a grace period until March 31, 2018 was recently added; some institutions have implemented the 8th edition in 2017
ICD-10 coding
  • C18.9 Malignant neoplasm of colon, unspecified
  • C21.8 Malignant neoplasm of overlapping sites of rectum, anus and anal canal
Primary tumor (pT)
  • TX: primary tumor cannot be assessed
  • T0: no evidence of primary tumor
  • Tis: carcinoma in situ, intramucosal carcinoma (involvement of lamina propria with no extension through muscularis mucosae)
  • 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:
    • 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 adheres to other adjacent organs or structures

Notes:
  • Tis and T1:
    • Tis in the AJCC 8th edition refers only to intramucosal carcinoma, a lesion with invasion into the lamina propria that does not penetrate the muscularis mucosa
    • Unlike in the 7th edition, lesions with high grade dysplasia without invasion into the lamina propria are not considered Tis and these lesions have no potential to spread
    • Term intraepithelial carcinoma is synonymous to Tis but is rarely used (and may be misleading)
    • True intramucosal carcinoma also lacks the potential for metastasis; however, because of the potential for missing invasion beyond the muscularis mucosa due to incomplete sampling, designating these lesions Tis is appropriate
    • T1 lesions have invasion into the submucosa
  • Carcinoma in a polyp:
    • Classified according to pT definitions used for colorectal carcinomas; i.e. invasive carcinoma in the muscularis mucosae or lamina propria is pTis and tumor that has entered the submucosa of the polyp's head or stalk is pT1
    • If a resected polyp has a clear margin during endoscopic resection, it is a pTis lesion and the nodal and metastatic status is unknown; however, the risk of metastatic disease is very low and lymph node dissection is not indicated
    • Several professional societies recommend resection if there is a high grade invasive tumor, the invasive tumor is 1 mm or less from the resection margin or lymphovascular space invasion is present
  • T4:
    • Separation of T4 into two categories (T4a and T4b) is based on different outcomes in expanded datasets
    • T4a tumors directly invade the serosal surface (visceral peritoneum)
      • This includes tumors with perforation where the tumor cells are continuous with the serosal surface through inflammation
      • Some but not all studies indicate that tumors that are under 1 mm from the serosal surface show a higher risk for peritoneal relapse; if so, multiple levels and additional sampling should be performed and if serosal surface involvement is not found, the tumor should be considered pT3
      • pT4a should not be used in nonperitonealized portions of the colorectum (posterior aspects of ascending and descending colon, lower rectum)
Regional lymph nodes (pN)
  • NX: regional lymph nodes cannot be assessed
  • N0: no regional lymph node metastasis
  • N1: metastasis in 1 - 3 regional lymph nodes
    • N1a: metastasis in 1 regional lymph node
    • N1b: metastasis in 2 - 3 regional lymph nodes
    • N1c: no regional lymph nodes are positive but there are tumor deposits in the subserosa, mesentery or nonperitonealized pericolic or perirectal / mesorectal tissues
  • N2: metastasis in 4 or more regional lymph nodes
    • N2a: metastasis in 4 - 6 regional lymph nodes
    • N2b: metastasis in 7 or more regional lymph nodes

Notes:
  • Minimum of 12 lymph nodes must be recovered for lymph node staging to be considered accurate in curative resections
  • Number of recovered nodes has been reported to correlate with better prognosis, likely due to more accurate staging
  • Metastasis to nonregional lymph nodes outside of the drainage area of the tumor, i.e. those not found along vascular arcades of the marginal artery or pericolonic, perirectal or mesorectal nodes should be considered distant metastasis (M1a)
  • A lymph node metastasis that in other sites would be considered a micrometastasis is recorded as a "typical" metastasis
    • Research is ongoing as to the possible significance of micrometastasis or metastasis only found with keratin staining
  • N1c tumor deposits are discrete tumor nodules of any shape, contour or size that lack associated lymph node tissue, vascular structures or neural structures found within the lymph drainage area of the primary carcinoma
    • These deposits are associated with poor overall survival
    • In cases with lymph node metastasis, the number of tumor deposits is NOT added to the number of positive lymph nodes
Distant metastasis (pM)
  • M0: no distant metastasis by imaging; no evidence of tumor in other sites or organs (this category is NOT assigned by pathologists)
  • M1: distant metastasis
    • M1a: metastasis confined to 1 organ or site without peritoneal metastasis
    • M1b: metastasis to 2 or more sites or organs is identified without peritoneal metastasis
    • M1c: metastasis to the peritoneal surface is identified alone or with other site or organ metastases

Notes:
  • Metastasis to nonregional lymph nodes outside of the drainage area of the tumor, i.e. those not found along vascular arcades of the marginal artery or pericolonic, perirectal or mesorectal nodes should be considered distant metastasis (M1a)
  • Multiple metastases in an organ, even paired organs (ovaries, lungs), are still M1a disease
  • Pathologist should not assign the global designation pM0, as metastasis unknown to the pathologist may be present
Prefixes
  • y: preoperative radiotherapy or chemotherapy
  • r: recurrent tumor stage
  • a: cancer discovered incidentally during autopsy
Grading of quality and completeness of the mesorectum in a total mesorectal excision
  • Complete: intact and smooth mesorectum, defects if present are no deeper than 5 mm, there is no coning and the circumferential resection margin is smooth and regular
  • Nearly complete: mesorectum is moderately bulky and irregular, defects on muscularis propria are visible, there is moderate coning and an irregular circumferential resection margin
  • Incomplete: mesorectum has little bulk, the muscularis propria is visible through defects, there is moderate to marked coning and an irregular circumferential resection margin
  • See J Clin Pathol 2007;60:849
Tumor regression after neoadjuvant therapy
Modified Ryan scheme for tumor regression score (only performed on primary tumor):
  • 0 (complete response): no viable cancer cells
  • 1 (near complete response): single cells or rare small groups of cancer cells
  • 2 (partial response): residual cancer with evident tumor regression but more than single cells or rare small groups of cancer cells
  • 3 (poor or no response): extensive residual cancer with no evident tumor regression
  • See CAP: Cancer Protocol Templates [Accessed 29 November 2017]

Notes:
  • In rectal cancer, the pathologic response to preoperative radiotherapy, chemoradiation or chemotherapy in colon or rectal cancer is important prognostically
  • Acellular mucin is considered to represent completely eradicated tumor and should not be used to assign pT category or be considered positive lymph nodes
Stage grouping

Stage 0: Tis N0 M0
Stage I: T1 - T2 N0 M0
Stage IIA: T3 N0 M0
Stage IIB: T4a N0 M0
Stage IIC: T4b N0 M0
Stage IIIA: T1 - T2 N1 / N1c M0
T1 N2a M0
Stage IIIB: T3 - T4a N1 / N1c M0
T2 - T3 N2a M0
T1 - T2 N2b M0
Stage IIIC: T4a N2a M0
T3 - T4a N2b M0
T4b N1 - N2 M0
Stage IVA: any T any N M1a
Stage IVB: any T any N M1b
Stage IVC: any T any N M1c
Prognostic tools for colon and rectum cancer meeting all AJCC quality criteria
Registry data collection variables (may or may not be responsibility of surgical pathologist)
  1. Tumor deposits: see above
  2. CEACAM5 (CEA) levels: preoperative blood levels recorded in nanograms per milliliter
  3. Tumor regression score: see above
  4. Circumferential resection margin: see above
  5. Lymphovascular invasion (LVI):
    • Tumor in a vessel wall or its remnant found with any stain is categorized as lymphovascular invasion (LVI) present
    • LVI should be subclassified as small vessel invasion ("L" lymphatic or small venule) or venous invasion ("V" tumor in an endothelial lined space with red blood cells or that is surrounded by smooth muscle)
  6. Perineural invasion: tumor identified in neural structures
  7. Microsatellite instability (MSI)
  8. KRAS and NRAS mutation: NRAS is similar to KRAS in structure and implications and is activated by somatic mutation in about 7% of colorectal carcinomas
  9. BRAF mutation
Histologic grade
  • GX: grade cannot be determined
  • G1: well differentiated
  • G2: moderately differentiated
  • G3: poorly differentiated
  • G4: undifferentiated
Histopathologic type
Historical staging systems no longer in use
Dukes staging:
  • Designed for rectum but was often applied to entire colon 
  • A: growth limited to wall of rectum
  • B: extension of growth to extrarectal tissues, no metastasis to regional lymph nodes
  • C: metastases in regional lymph nodes, modified in 1935 to C1 and C2 stages
    • C1: metastases to regional lymph nodes
    • C2: metastases to lymph nodes at point of mesenteric blood vessel ligature
  • D: distant metastases (not part of original classification)

Astler-Coller classification:
  • A: lesion limited to mucosa
  • B1: lesion involves muscularis propria but does not penetrate through it
  • B2: lesion penetrates through the muscularis propria
  • C1: metastatic tumor in lymph nodes but the tumor itself is still confined to the bowel wall
  • C2: metastatic tumor in lymph nodes and tumor itself has penetrated through the entire bowel wall 

  • Per Rosai, call stage B if no identifiable muscularis propria layer between tumor and serosal surface
Diagrams / tables

Images hosted on other servers:

Staging related diagrams from AJCC 7th edition (2006)

Clinical images

Images hosted on other servers:

Sentinel lymph nodes

Microscopic (histologic) images

Images hosted on other servers:

Sentinel lymph nodes

Board review question #1
Patient with colon cancer has been found to have 2 positive regional lymph nodes and 1 tumor deposit in the subserosa. What is the correct pN staging?

  1. N1b, metastases in 2 - 3 regional lymph nodes
  2. N1c, tumor deposits in the subserosa, mesentery or nonperitonealized pericolic or perirectal / mesorectal tissues
  3. N2a, metastases in 4 or more regional lymph nodes
Board review answer #1
A. N1b, metastases in 2 - 3 regional lymph nodes. N1c is used only if there are no lymph node metastases. The number of tumor deposits is NOT added to the number of positive lymph nodes if positive lymph nodes exist.
Board review question #2
Patient presenting with rectal bleeding is found to have an adenocarcinoma of the sigmoid colon; an enlarged axillary lymph node is also detected. He undergoes left hemicolectomy and biopsy of the axillary lymph node. He is found to have adenocarcinoma that invades into pericolonic tissue without penetrating the visceral peritoneum and 8 regional lymph node metastases, as well as metastases in the axillary lymph node. What is the pTNM staging?

  1. T2N2
  2. T3N2
  3. T3N2M1
  4. T4N2
Board review answer #2
C. T3N2M1. Tumor that invades through the muscularis propria into the pericolorectal tissues without penetrating the visceral peritoneum is T3. Metastases to 7 or more regional lymph nodes is N2. Lymph nodes outside of the drainage area of the primary tumor should be considered distant metastasis (M1a).