Other Pathology

Predisposing conditions

Inflammatory: ulcerative colitis/Crohn's disease (1% of colorectal carcinoma), schistosomiasis, juvenile polyposis syndrome (10% risk). Carcinoma in ulcerative colitis occurs in patients with quiescent disease of pancolic distribution and long duration (>10-20 years). It may be associated with preceding or concurrent mucosal dysplasia above, adjacent to or distant from the tumour. A rectosigmoid biopsy positive for mucosal dysplasia is an indicator of the possible presence of carcinoma somewhere in the colorectum. Carcinomas may be multiple, right-sided and in up to one-third of cases difficult to define on endoscopic and gross examination. This is due to aberrant growth patterns with tumour arising in polypoid, villous or flat mucosal dysplasia in a background of mucosa already distorted by the effects of chronic inflammation, e.g. inflammatory polyps and strictures. Therefore interval colonoscopic biopsy of flat mucosa and target biopsy of possible DALMs (dysplasia associated lesion or mass) is employed to detect dysplasia as a marker of potential carcinoma which may be occult and submucosal in location. Due to variation in observer reproducibility, mucosal dysplasia should be assessed by two experienced pathologists according to Riddell and/or the Vienna classification. In the absence of a DALM low-grade dysplasia may be followed up by colonoscopy, whereas persistent low-grade dysplasia, DALM-asso-ciated dysplasia or high-grade dysplasia should be considered for colec-tomy. Surface overexpression of Ki-67 and p53 is usual in a high-grade dysplasia and may help to distinguish from florid regenerative changes. Distinction from a sporadic adenoma in a colitic patent is usually made by the absence of dysplasia in the flat mucosa adjacent to and away from the lesion. Prognosis is variable as some lesions present late masked by the symptoms of ulcerative colitis and others are found early at regular (annual/biennial after 8-10 years' disease duration) surveillance colonoscopy.

Neoplastic: aberrant crypt foci (adenomatous, or, serrated ± dysplasia), adenoma(s), familial adenomatous polyposis coli (and the related Gardner's syndrome), previous or synchronous carcinoma(s), HNPCC (see below), hyperplastic polyposis (rare).

The usual dysplasia-carcinoma sequence indicates that development of adenocarcinoma increases with the size of adenoma, its degree of villous architecture and grade of dysplasia, multiplicity of lesions and age of the patient. A maximum diameter >2 cm and villous morphology confer approximate cancer risks of 50% and 40%, respectively. These risk factors in a rectal adenoma are also good indicators in individual patients for full colonoscopic survey and follow-up to detect right-sided colonic neoplasms.

In the UK severe or high-grade dysplasia is applied to epithelial proliferation of any degree of complexity that is mucosa based, i.e. above the muscularis mucosae. Adenocarcinoma is reserved for those lesions that show invasion below the muscularis mucosae. Terms such as carcinoma in situ tend to be avoided due to the relative lack of mucosal lymphatics, the rarity of nodal metastases with such lesions and the fear of over-treatment with unnecessary radical resection. However, it is not always possible to demonstrate invasion through the muscularis mucosae on biopsy and malignant epithelial changes with a desmoplas-tic stromal response are sufficient for a designation of adenocarcinoma. Sampling error must always be borne in mind in that a dysplastic fragment may not show the adjacent invasive component. Undoubtedly there are also malignant polyps for which terminology such as carcinoma in situ or intramucosal carcinoma is appropriate. In these circumstances there should be active discussion with the surgeon, emphasizing that the process is "mucosa-confined" and comments made on the adequacy of local excision. It should also be checked that the specimen is a complete polypectomy and not simply a diagnostic biopsy from the edge of a larger lesion.

0 0

Post a comment