Adenocarcinoma of the Colon and Rectum
Grading / Staging / Report
Grading
- Grading based on worst area
- Leading front of invasion excluded from grading
- It is acceptable to grade simply as Low vs. High grade
- Applies only adenocarcinoma NOS
- See special types for relevant grading criteria (mucinous, signet ring, medullary, squamous)
- Low grade ≥50% gland forming
- Well differentiated
- >95% gland forming
- Moderately differentiated
- 50-95% gland forming
- Any MSI-H carcinoma
- High grade <50% gland forming
- Poorly differentiated
- 0-49% gland forming
- Staging
- Use TNM staging
- Problematic issues in T staging
(see also miscellaneous issues below)
- Tis
- Includes high grade intraepithelial dysplasia and intramucosal carcinoma
- Includes invasion into but not through muscularis mucosae
- T3 (invasion through muscularis propria into subserosa or pericolic and perirectal tissues)
- Absence of smooth muscle between advancing edge of carcinoma and the surrounding soft tissue counts as pT3
- A nodule of carcinoma in the pericolic fat that lacks continuity with intramural invasive carcinoma should be considered as a Tumor Deposit (see lymph nodes below)
- Such a nodule does not constitute evidence of T3
- T4a (tumor penetrates visceral peritoneum)
- Any of the following 3 criteria qualify
- Carcinoma at surface with mesothelial inflammation/hyperplasia or ulceration
- Free carcinoma cells on surface with underlying ulceration of peritoneum
- Positive cytology scrape preparation taken from the serosal surface
- Proposed but not widely accepted
- Mesothelial inflammatory/hyperplastic response with carcinoma cells close to surface
- Any of the following 3 criteria qualify
- T4b (invasion of other organs or structures)
- Longitudinal spread to adjacent bowel sites (e.g. terminal ileum) is not pT4a
- Direct invasion through the bowel wall into another GI site does qualify
- Longitudinal spread to adjacent bowel sites (e.g. terminal ileum) is not pT4a
- Multiple simultaneous carcinomas
- Includes those diagnosed within 2 months
- Includes Tis lesions
- TNM should be reported for the lesion with the highest T score
- Add (m) or (2) etc. to indicate multiple or number of primary lesions e.g. pT3(m)
- Margin evaluation
- Proximal and distal margins
- Histologic evaluation optional if grossly >5 cm
- Circumferential / radial margin applies to rectum and non-peritonealized surfaces of colon
- Does not apply to peritoneal surface
- In colon with a mesentery
- Mesenteric margin is the radial margin
- It is not applicable if the carcinoma is anti-mesenteric
- When grossing in, the location relevant to the mesentery should be noted
- When applicable, the distance should be given
- For rectal resections, the mesorectal tissue should be evaluated for the following
- Surface of resection
- Intact surface
- Defects >5 mm but not extending to muscularis propria
- Defects in surface extending to muscularis propria
- Bulk of mesorectal tissue should be noted
- Tis
- Problematic issues in N staging
(see also miscellaneous issues below)
- Direct invasion of a node by the carcinoma counts as nodal involvement
- Only regional draining nodes count for N staging
- Nodes draining other bowel areas count towards M staging
- If the primary spreads longitudinally to an adjacent bowel area, nodes draining that area count towards N staging
- Involvement only of afferent lymphatics in a node counts as pL1, not as pN1
- Nodules in the extra-tumoral soft tissue, discontinuous from intramural carcinoma:
- (If there is any evidence of residual lymph node, they should be considered nodal metastases)
- They should be recorded as Tumor Deposits (pTD)
- They are not counted as nodes
- They do not constitute evidence of pT3
- If no lymph nodes are involved by carcinoma, these tumor deposits qualify for pN1c
- If nodes are involved, they are not designated pN1c and have no impact on TNM
- pN1c affects the overall Stage Group in the same manner as pN1a and b
- This applies only to deposits within the lymphatic drainage of the tumor
- Thus Tumor Deposits function as nodal metastases in staging when they are needed, but do not contribute to your node count
- Circumscribed vs. stellate contour is no longer a criterion
- Isolated tumor cells (ITC) in lymph nodes
- Defined as either:
- Detectable only by special techniques, or
- If identified on H&E, ≤0.2 mm each cluster, even if multiple
- Defined as negative for TNM purposes but indicate as appropriate if present:
- pN0(i+) = morphologic or immunohistologic ITC present
- pN0(m+) = molecular evidence of ITC
- Report should state number of nodes with ITC and that the biologic significance is presently unknown
- Routine use of special studies for detection of ITC is not currently recommended
- Clusters of cells ≥0.2 mm but <2 mm are considered micrometastases and designated as positive for TNM
- Defined as either:
- Problematic issues in M staging
(see also miscellaneous issues below)
- Isolated tumor cells (ITC) in distant organs (e.g. bone marrow)
- Same definitions and recommendations as above for lymph nodes
- The following all count as pM1
- Involvement restricted to lymphatics in a distant organ
- Involvement of non-regional lymph nodes
- Involvement of peritoneal surface away from the leading edge of the tumor
- Involvement of peritoneal surface of other intra-abdominal structures and organs
- Peritoneal fluid positivity
- Lateral spread or mucosal skip lesions in adjacent bowel sites does not count as pM1
- Absence of carcinoma in any examined site does not constitute pM0
- A 0 designation is only applicable to autopsies and is recorded as aM0
- Isolated tumor cells (ITC) in distant organs (e.g. bone marrow)
- Miscellaneous issues
- Post-neoadjuvant therapy excision specimens
- TNM as usual but add prefix, e.g. ypT1
- Size is based on dimensions of residual viable tumor, not the scar or mucin pools
- Pools of mucin without epithelial cells are counted as negative at both the primary site and in lymph nodes (Shia 2011)
- Residual tumor in patient at end of surgical excision
- Either distant or at positive surgical margin
- Positive margin generally is interpreted as indication of residual neoplasm but should be discussed with surgeon
- Designate as R1 if microscopic
- Designate as R2 if macroscopic
- Either distant or at positive surgical margin
- Recurrences
- Coded as rpT1 etc.
- Use usual TNM guidelines as for primary
- Label recurrence as located in proximal segment of anastomosis, except when that is ileum following a right colon resection
- Post-neoadjuvant therapy excision specimens
