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
- Surveillance may be altered (see Colorectal Adenoma Clinical discussion)
- 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% |
- 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
