Neoplastic Conditions

Simple hyperplastic or metaplastic polyps are benign and more prevalent in the left colon with increasing age. They are sometimes associated with malignancy if sessile, right sided and incorporating a degree of epithelial dysplasia (serrated adenoma). Adenomatous polyp is the commonest precancerous lesion.

Adenoma: designated as tubular, tubulovillous or villous depending on the relative proportions of glands and fronds present and composed of low- or high-grade dysplastic epithelium. Increasing in frequency with age and in the left colon the risk of malignancy relates to the size (> 2 cm = 40-50% risk), degree of villous morphology and grade of dysplasia. Tubular adenomas are nodular and tend to develop a distinct stalk whereas villous lesions are sessile. Stalked adenomas can twist and prolapse resulting in glandular herniation into the submucosa that mimics invasive carcinoma - the presence of haemosiderin and lack of stromal fibrous desmoplasia are useful histological clues. Invasive carcinoma is defined by the presence of neoplastic epithelium infiltrating submucosa and in stalked adenomas polypectomy may be considered therapeutic if the tumour is well-to-moderately differentiated, does not show lympho-vascular invasion or involvement of the diathermied base. Otherwise, colonic resection is required, and, therefore, good orientation of the adenoma to its stalk and assessment of the base are crucial. In contrast, invasion in a sessile adenoma accesses true mural submucosa and colonic resection is usually considered more appropriate unless the patient is very elderly or medically unfit. Local mucosal resection is an option but further radical surgery is required if the cancer involves muscle coat, the base of the specimen, lymphovascular channels or is poorly differentiated.

It is not unusual for patients to have several adenomas but in FAPC there are hundreds or thousands with progression to colorectal cancer 20-30 years earlier than average. There is also a strong association with duodenal adenomas and periampullary carcinoma.

Flat adenomas are less common and difficult to identify macroscopically without the use of a hand lens or dye spray technique. They have proportionately higher grades of dysplasia and frequency of carcinoma and may account for a proportion of the 30% of carcinomas without an identifiable adenoma at their edge.

Adenocarcinoma: comprising the vast majority of colorectal malignancies, 80-85% are moderately differentiated adenocarcinoma of no special type. A minority are mucinous, signet ring cell or poorly differentiated. Distribution is throughout the colorectum although rectosigmoid is the commonest site (50% of cases) - 10-15% of sporadic cases are multiple occurring either synchronously or subsequently. Predisposing conditions are chronic ulcerative colitis, FAPC and hereditary non-polyposis colorectal cancer (HNPCC). In HNPCC there is a tendency for right-sided cancers - which may be multiple, mucinous or poorly differentiated - and a family history of cancer at a younger age, also involving other sites, e.g., stomach, uterus, ovary, kidney and breast. Its genetic basis is different from that of sporadic colorectal cancer due to a deficiency in the DNA mismatch repair genes.

As previously noted, the cancer site and its macroscopic growth pattern influence clinical presentation. Important prognostic indicators are the extent of local tumour spread, a circumscribed or infiltrative margin, involvement of the serosa, longitudinal or mesocolic/mesorectal resection margins and tumour perforation. Tumour present to within < 1 mm defines involvement of the mesenteric margin irrespective of whether it is nodal, lymphovascular or direct spread. Generally, a macroscopic clearance of 2-3 cm from a longitudinal margin is satisfactory unless histology shows the cancer to be unusually infiltrative or poorly differentiated. A minimum target of eight but preferably all mesenteric lymph nodes should be counted and sampled and a suture tie limit node identified - in some colectomy specimens this may mean more than one. Involvement of adjacent organs or structures (e.g., abdominal wall) is documented and predisposing lesions such as adenoma(s) or colitis represented. Multiple tumours are dissected and staged individually with respect to mural and nodal spread.

Other cancers: carcinoid tumours are usually small, incidental, mucosal polyps; GISTs are rare and malignant lymphoma can complicate ulcerative colitis or AIDS.

Prognosis: relates mainly to the depth of tumour spread, lymph node involvement and adequacy of local excision with overall five-year survival 35-40%. Cancers confined to the mucous membrane or wall do much better than those that invade beyond this or show nodal disease. Adverse prognostic indicators also include a mucinous character, poor differentiation, tumour perforation, obstruction and resection margin involvement. It is estimated that about 50% of patients are cured, 10% die from local recurrence and 40% from lymphatic and vascular spread. Treatment is surgical excision with adjuvant chemotherapy for cancers showing poor differentiation; nodal, peritoneal and extramural vascular spread; tumour perforation or resection margin involvement. Rectal cancers often receive five-day, short-course, preoperative radiotherapy in an attempt to downstage the lesion or facilitate resection - this usually does not produce the marked macroscopic and histological features of regression that can be seen with the alternative six-week-long course of adjuvant therapy that is given to clinically fixed tumours.

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