Usually significant architectural and/or cytologic atypia
Usually lacks significant architectural and/or cytologic atypia (high grade dysplasia may be misplaced occasionally but is typically accompanied by bland adenoma tissue)
Desmoplastic stroma
Inflammatory or fibrotic stroma
Infiltrates through muscularis mucosae
Frequently demonstrable continuity with surface through a gap in the muscularis mucosae
Hemosiderin restricted to head of polyp
Hemosiderin common in stalk stroma
Glands not accompanied by lamina propria
Glands may be accompanied by lamina propria
Usually infiltrative, non-circumscribed
Frequently circumscribed
May occur throughout the colorectum
Virtually restricted to left colon
Collagen type IV weak, discontinuous
Collagen type IV strong, continuous around epithelial nests
E cadherin markedly decreased staining compared to overlying adenoma
E cadherin same intensity as overlying adenoma (high grade dysplasia may show decrease)
Prominent lymphoid infiltrate in virtually all cases
Lymphoid infiltrate variable
Grading / Staging
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
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
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
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
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
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
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
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