**2. Malignant polyps**

Not all polyps are created equal. The adenoma carcinoma sequence has long been recog‐ nised as the natural history of colorectal carcinoma and it is therefore logical that some ade‐ nomas will be discovered with foci of malignancy within them.

For those confined to the mucosa, polyps showing foci of potentially malignant cells are of‐ ten termed *carcinoma in situ*. The lack of lymphatics in the mucosa prevents distant spread and, as these lesions are neither regarded as malignant or treated as malignancies, the term high grade mucosal neoplasm is now preferred. [4]

© 2013 Taylor and Hosie; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

The definition of colorectal carcinoma is dysplasia crossing the *muscularis mucosa,* so when high grade dysplasia in these polyps crosses this barrier the lesion is termed a malignant polyp. A malignant polyp is essentially a macroscopically benign lesion that contains malig‐ nant foci on further examination. When the totality of the polyp is comprised of malignancy the term polypoid carcinoma is often used.

whereas only 10% of pedunculated polyps were similarly classified.[11] One meta-analysis reported positive resection margins in 56.8% of sessile lesions verses 18.7% in polypoid le‐

Size and tubular or villous architecture are also well known to affect the malignant potential of polyps. However, in a similar fashion to flat or depressed areas of dysplasia, very large

Polyps are defined by dysplasia and the varying degree displayed by different polyps is

Noninvasive carcinoma (4-2)

Suspicious for invasive carcinoma (4-3)

Intramucosal carcinoma (lamina propria invasion) (4-4)

The Malignant Polyp: Polypectomy or Surgical Resection?

http://dx.doi.org/10.5772/52865

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polyps are seldom excised endoscopically and are not relevant to the current topic.

thought to explain a large degree of their different metastatic potential.[14]

**Table 2.** Revised Vienna classification of epithelial neoplasla for esophagus, stomach, and colon. [13]

The revised Vienna classification is widely used to define the degree of dysplasia colorectal polyp. By definition malignant polyps are 4-4. For colorectal carcinomas the WHO classifica‐ tion recognises 4 grades of differentiation, with G1 representing well differentiated, through moderate (G2) and poorly differentiated (G3) to undifferentiated (G4). G1-2 are convention‐

In a meta-analysis of published series, Hassan *et al.*[1] reported a 3.9 (1.9-8.4) odds ratio for no‐ dal metastasis with regard to high vs low grade malignant polyps. The odds ratio for mortality was reported as 9.2 (4.7-18.2). Determining the exact risk from high grade dysplasia is compli‐ cated by their relative rarity. One study of 80 malignant polyps found only 2 poorly differenti‐

It is interesting to note that despite poor differentiation being recognised as an important determinant of nodal disease, no universally accepted definition exists. Indeed in studies where the prevalence of highly dysplastic lesions was lower, the risk of nodal disease in these polyps was increased. (See Table 3). This suggests that poor differentiation, when a rigorous definition is used is an extremely important predictor of nodal disease. Those stud‐ ies that did not find the degree of dysplasia to be significant are hampered by the very small

ated polyps.[12] In a meta-analysis 7.2% of 1612 malignant polys were high grade.[1]

Low-grade Intraepithelial neoplasia. Adenoma/dysplasia High-grade neoplasia (intraepithelial or intramucosal) Adenoma/dysplasia (4-1

ally regarded as low grade and G3-4 as high grade.

number of highly dysplastic lesions in their sample.

sions (P < 0.0001).

**3.2. Grading**

Negative for Intraepithelial neoplasia. Indefinite for Intraepithelial neoplasia.

Submucosal carcinoma

T1 lesions are therapeutically significant as they are the first lesions where nodal and distant metastases must be considered. The management of these polyps is based on the belief that the risk of spread can be stratified according to the histology of the resected polyp.[5] In the past authors used various criteria to define favourable or unfavourable histology and guide management.[1,2,6,7] For a large part, this has involved dividing patients into two groups. A "low risk" group, who are safe without further treatment and a "high risk group", for whom surgery should be considered.[8,9] Unfortunately published studies disagree about the factors that are most significant.[3,10-12]
