Colon

• 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)

• 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

• 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

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 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

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

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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

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.

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Reference: Staging-carcinoma

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

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).

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Reference: Staging-carcinoma