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Colorectal Adenoma Containing Invasive Adenocarcinoma

Definition

  • Adenocarcinoma arising in an adenoma of the colon or rectum

Alternate/Historical Names

  • Malignant adenoma
  • Malignant polyp

Diagnostic Criteria

  • Carcinoma may be found within an adenoma resected endoscopically
    • This raises questions about the need for subsequent therapy, including surgery
  • High grade dysplasia / intramucosal carcinoma is excluded from this discussion
    • Probability of lymph node metastases or adverse cancer related outcome is essentially zero
    • If margins of resection are clear of high grade dysplasia, no further therapy is required for the lesion
    • The significance of intramucosal invasive carcinoma with high grade features is currently a subject of debate (see Colorectal Adenoma Grading)
  • Carcinoma is defined as invasion through the muscularis mucosae
  • Risk of carcinoma is related to the size of the adenoma
Adenoma Size % with Adenocarcinoma
≤5 mm Essentially 0%
6-15 mm 2%
16-25 mm 19%
26-35 mm 43%
>35 mm 76%
(Nasco 1997)
  • In the absence of the adverse features described below, polypectomy is sufficient treatment for adenomas containing invasive carcinoma
  • Adverse outcomes (local recurrence, lymph node metastases, cancer related mortality) are significantly increased if any of the following are present:
    • Carcinoma present at or within 1 mm of the surgical margin
      • Usually recognized by cautery
        • Measure from the superficial edge of the cautery where tissue is still recognizable
    • High grade carcinoma (see Grading at left), even if only focal in the lesion
    • Vascular invasion
      • Some studies show this not to be an independent variable
  • For non-rectal sessile lesions, depth of invasion of submucosa may be important
    • Invasion limited to the superficial 2/3 of submucosa has virtually zero% incidence of adverse outcome
    • This may not be assessable if muscularis propria is not in the specimen
    • The same may be true of polypoid lesions, but they are only very rarely resected to the level of the underlying natural submucosa
  • For rectal sessile lesions, any submucosal invasion has a risk of adverse outcome
  • Haggitt levels have been proposed as descriptors of the level of invasion
    • For polypoid lesions
Level 0 Intramucosal carcinoma only
Level 1 Invasion into the submucosa of the head of the polyp, surrounded on all surfaces by adenoma or carcinoma
Level 2 Invasion to the junction of the head and neck
Level 3 Invasion into submucosa of stalk, surrounded on all surfaces by non-neoplastic mucosa
Level 4 Invasion into the level of the native submucosa
  • Sessile lesions with invasion through the muscularis mucosae are Level 4 by definition
  • No clinically useful information is conveyed by these levels that is not already provided by the above described determinants of adverse outcome
    • Levels 1,2 and 3 are associated with virtually 0% adverse outcome unless the above adverse determinants are present
    • Level 4 is virtually never present in a polypoid resection specimen because of snare removal
    • Level 4 involvement is equivalent to submucosal invasion as described above for sessile lesions

Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342

Original posting : 1/31/10

Supplemental studies

Immunohistology

  • Smooth muscle actin stain may be useful for demonstrating level of invasion
  • E cadherin shows markedly decreased staining in invasive areas
  • Collagen type IV staining is weak and discontinuous around invasive areas

Differential Diagnosis

Colorectal Adenoma Containing Invasive Adenocarcinoma Colorectal Adenoma with Benign Misplacement of Glands / Pseudoinvasion
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)

Grading / Staging

  • It is acceptable to grade simply as Low vs. High grade
    • Low grade ≥50% gland forming
      • Well differentiated
        • >95% gland forming
      • Moderately differentiated
        • 50-95% gland forming
    • High grade <50% gland forming
      • Poorly differentiated
        • 5-49% gland forming
        • Signet ring (>50% of cells signet ring)
      • Undifferentiated
        • <5% gland forming
  • Use TNM staging
    • Lesions should be staged if the margins of resection are clear
    • Provisional stage may be given if margins are involved but should be clearly indicated as provisional
    • An adenoma containing only high grade dysplasia or intramucosal carcinoma is pTis
    • An adenoma containing carcinoma invasive into the stalk is pT1 (unless it invades into muscularis propria)

Bibliography

  • Risio M, Fiocca R. Malignant adenoma: diagnosis, staging, risk factors, lymph node involvement and problems of sampling. Tech Coloproctol. 2004 Dec;8 Suppl 2:s253-6.
  • Coverlizza S, Risio M, Ferrari A, Fenoglio-Preiser CM, Rossini FP. Colorectal adenomas containing invasive carcinoma. Pathologic assessment of lymph node metastatic potential. Cancer. 1989 Nov 1;64(9):1937-47.
  • Nivatvongs S. Surgical management of malignant colorectal polyps. Surg Clin North Am. 2002 Oct;82(5):959-66.
  • Hassan C, Zullo A, Risio M, Rossini FP, Morini S. Histologic risk factors and clinical outcome in colorectal malignant polyp: a pooled-data analysis. Dis Colon Rectum. 2005 Aug;48(8):1588-96.
  • Nusko G, Mansmann U, Partzsch U, Altendorf-Hofmann A, Groitl H, Wittekind C, Ell C, Hahn EG. Invasive carcinoma in colorectal adenomas: multivariate analysis of patient and adenoma characteristics. Endoscopy, 1997 Sep;29(7):626-31.
  • Lewin MR, Fenton H, Burkart AL, et al. Poorly differentiated colorectal carcinoma with invasion restricted to lamina propria (intramucosal carcinoma): a Follow-up Study of 15 cases. Am J Surg Pathol. 2007;31:1882-1886.
  • Shia J; Klimstra DS. Intramucosal Poorly Differentiated Colorectal Carcinoma: Can it be Managed Conservatively? Am J Surg Pathol. 2008 Oct;32(10):1586-1588.
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