Colon

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• pTX: cannot be assessed
• pT0: no evidence of primary tumor
• pTis: carcinoma in situ, intramucosal carcinoma (involvement of lamina propria with no extension through muscularis mucosae)
• pT1: tumor invades submucosa (through the muscularis mucosae but not into the muscularis propria)
• pT2: tumor invades muscularis propria
• pT3: tumor invades through the muscularis propria into the pericolorectal tissues
• pT4:
  • 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:

• pTis
  • Tis (carcinoma in situ) refers to intramucosal carcinoma, which invades into the lamina propria and may involve but not penetrate through the muscularis mucosae (Ann Surg Oncol 2018;25:1454)
  • Intraepithelial carcinoma is synonymous with high grade dysplasia and should not be assigned to Tis, as these lesions lack potential for tumor spread (American Joint Committee on Cancer: AJCC Cancer Staging Manual, 8th edition, 2017)
  • Tumor extension through the muscularis mucosae into the submucosa is classified as pT1; a synoptic report is required for all cancers that are pT1 and beyond but not for pTis tumors
  • Tis includes intraepithelial carcinoma (tumor confined to epithelium by basement membrane) and intramucosal carcinoma (carcinoma invading lamina propria)
• Carcinoma in polyps
  • Polyps with carcinoma are staged according to pT definitions for colorectal carcinomas
    • Polyps with invasive carcinoma confined to muscularis mucosae are pTis and pT1 if invasive component extends into submucosa of polyps' head or stalk
    • Polyps with carcinoma invading the submucosa (pT1) and beyond are considered malignant polyps
    • Surgical resection is recommended for malignant polyps that contain high grade carcinoma, invasive carcinoma ≤ 1 mm from the resection margin or have lymphatic / venous vessel invasion (Arch Pathol Lab Med 2019;143:1450, American Joint Committee on Cancer: AJCC Cancer Staging Manual, 8th edition, 2017)
    • High tumor budding is also an adverse prognosticator in malignant polyps CAP: Protocol for the Examination of Resection Specimens From Patients With Primary Carcinoma of the Colon and Rectum [Accessed 20 September 2023])
• pT4
  • If the tumor is grossly / macroscopically adherent to other organs, it is cT4; if no tumor is found microscopically within the adhesion, it should be best classified as pT3 with a note
  • Separation of T4 into 2 categories (T4a and T4b) is based on different outcomes in multiple 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 and when tumor is present at the ink in serosal cleft
    • Even in the absence of readily demonstrable tumor cells on the serosal surface in histologic sections, grossly perforated cancers should be assigned pT4a stage (Surg Pathol Clin 2017;10:961)
    • Some but not all studies indicate that tumors that are < 1 mm from the serosal surface show a higher risk for peritoneal relapse
      • Multiple levels and additional sampling should be performed
      • In the absence of serosal surface involvement, the tumor should be considered pT3 (Mod Pathol 2021;34:131)
    • Utility of elastic stain to assess the peritoneal involvement is not universally accepted due to discontinuity of elastic lamina in colonic peritoneum (particularly absent in right colon) as well as difficulties in interpreting the stain (Mod Pathol 2015;28:S95)
    • pT4a should not be used in nonperitonealized portions of the colorectum (posterior aspects of ascending and descending colon, lower rectum)
  • T4b: transmural extension into another organ or site is a must for T4b designation; intramural extension of tumor from a segment of the large intestine into an adjacent subsite does not affect the pT classification

• pNX: cannot be assessed
• pN0: no regional lymph node metastasis
• pN1: 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
• pN2: 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 or likely from implying better host response
• N category is limited to only the regional nodes that are in the lymphatic drainage area of the tumor; metastasis to lymph nodes not found along vascular arcades of the marginal artery or pericolonic, perirectal or mesorectal nodes should be considered distant metastasis (M1a)
• Lymph nodes with micrometastasis (0.2 - 2 mm) as well as macrometastasis (> 2 mm) are considered positive
• Isolated tumor cells (single tumor cells or groups < 0.2 mm in maximum dimension) are classified as N0 as they were found to have no adverse prognosis (Eur J Surg Oncol 2014;40:263)
• Tumor deposits are discrete tumor nodules of any shape, contour or size that lack associated lymphoid tissue, vascular structures or neural structures found within the lymph drainage area of the primary carcinoma
• Only in the absence of unequivocal lymph node metastases, tumor deposits are recorded as N1c; in cases with lymph node metastasis, the number of tumor deposits is not added to the number of positive lymph nodes
• There is no consensus opinion on assigning lymph nodes with acellular mucin pool deposits as positive (N1) or negative (N0) (Mod Pathol 2020;33:153)

• 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 (Ann Surg Oncol 2018;25:1454)
  • 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 lymph nodes outside of the drainage area of the tumor (nonregional lymph 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

• c: clinical (cTNM)
• p: pathological (pTNM)
• y: postneoadjuvant chemoradiation therapy (ycTNM or ypTNM)
• r: recurrent tumor stage (rTNM)
• a: cancer discovered incidentally during autopsy (aTNM)

Notes:

• Current clinical practice involves neoadjuvant chemoradiation for cT3 and cT4 rectal cancers
• Microscopic evidence of residual disease has been shown to be associated with better prognosis than gross residual disease, which mandates thorough sectioning of specimens from neoadjuvant treated cancers
• Tumor regression should be assessed in the primary tumor and not based on nodal metastasis assessment
• Although acellular mucin is considered to represent completely eradicated tumor and recommendations are not to use mucin pools without viable tumor cells in assigning pT or pN category, there seems to be lack of consensus among pathologists across the world (Mod Pathol 2020;33:153)
• When the mucin pools are present at the radial margin without any viable cells, the practice among most pathologists is to render the margin status negative (Mod Pathol 2020;33:153)

Contributed by Vidya Arole, M.D.

Contributed by Vidya Arole, M.D. and Wei Chen, M.D.

Which of the following findings corresponds to T1 pathological stage (pT1) in colorectal carcinoma?

1. Polyp with high grade dysplasia and no invasion
2. Tumor invading and limited to lamina propria
3. Tumor invading into muscularis mucosae
4. Tumor invading through muscularis mucosae into submucosa

D. Tumor invading through muscularis mucosae into submucosa. Answers B and C are incorrect because tumor invasion that is limited to lamina propria and invasion into muscularis mucosae describe pTis. Answer A is incorrect because a polyp with high grade dysplasia and no invasion is not invasive carcinoma.

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Reference: Colon - Staging-carcinoma

What is the pathologic stage for this ascending colon cancer based on the above images?

1. pT1
2. pT2
3. pT3
4. pT4

A. pT1. The tumor is invading and confined to the submucosa. Note the tumor glands are next to the thick walled vessels of the submucosa. Answer B is incorrect because pT2 would be tumor invading into (but not through) the muscularis propria. Answer C is incorrect because pT3 would be tumor invading through the muscularis propria into the pericolorectal soft tissue. Answer D is incorrect because pT4 would be invasion of serosa or adjacent structures.

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Reference: Colon - Staging-carcinoma