Tumour spread and staging

Following transmural extension through the muscularis propria into pericolic or perirectal soft tissue, the tumour may involve contiguous structures. The consequences of direct extension depend on the anatomic site. An advanced rectal carcinoma may extend into pelvic structures such as the vagina and urinary bladder, but cannot gain direct access to the peritoneal cavity when it is located distal to the peritoneal reflection. By contrast, colonic tumours can extend directly to the serosal surface. Perforation can be associated with transcoelomic spread to the peritoneal cavity (peritoneal carcinomatosis). Involvement of the peritoneal surface should only be diagnosed if the peritoneum is ulcerated or if tumour cells have clearly penetrated the mesothelium. Since the peritoneal surface infiltrated by tumour cells may become adherent to adjacent structures, direct extension into adjoining organs can also occur in colonic carcinomas that have invaded the peritoneal portion of the wall {62}. Implantation due to surgical manipulation occurs only occasionally, but has been reported after laparoscop-ic colectomy for cancer {1106}. Spread via lymphatic or blood vessels can occur early in the natural history and lead to systemic disease. Despite the presence of lymphatics in the colorectal mucosa, lymphogenic spread does not

Fig. 6.11 Crohn-like lymphoid reaction associated with a colonic adenocarcinoma.

occur unless the muscularis mucosae is breached and the submucosa is invaded, This biological behaviour stands in sharp contrast to carcinomas of the stomach where metastasis occurs occa

Fig. 6.12 A Well differentiated adenocarcinoma. B Moderately diffferentiated adenocarcinoma. C Poorly differentiated adenocarcinoma; this lesion was MSI-H and shows numerous intraepithelial lymphocytes. D Undifferentiated carcinoma.

sionally from purely intramucosal carcinomas. Invasion of portal vein tributaries in the colon and vena cava tributaries in the rectum can lead to haematogenous dissemination.

Staging

The classification proposed by C. Dukes in 1929-35 for rectal cancer serves as the template for many staging systems currently in use. This family of classifications takes into account two histopatho-logical features: depth of penetration into the wall and the presence or absence of metastasis in regional lymph nodes. The TNM classification {66} is replacing the Dukes classification.

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