TUMORS OF THE LARGE INTESTINE

Benign

Polyp – a clinical description of any elevated tumor.

Polyps can occur:

  • Singly
  • Synchronously in small numbers or
  • As part of a polyposis syndrome

In familial adenomatous polyposis (FAP), >100 adenomas are present.

Adenomatous polyps

Classification of polyps of the large intestine

Adenomatous polyps vary from tubular adenoma rather like raspberry on a stalk, to the villous adenoma, a flat spreading lesion.

Solitary adenomas are usually found during the investigation of colonic bleeding or sometimes fortuitously.
Villous tumors more usually give symptoms of

  • Diarrhoea
  • Mucus discharge
  • Occasionally hypokalaemia

Risk of malignancy developing in an adenoma increases with increasing size of tumor.

Adenomas larger than 5mm in diameter are usually treated because of their malignant potential. Colonoscopy snare polypectomy click here or diathermy obliteration with hot biopsy forceps click here can be used.

Huge villous adenomas of the rectum can be difficult to remove even with techniques per anus, and occasionally protectomy click here is required ; the anal sphincter can be preserved.

Proctectomy is a surgery to remove all or part of the rectum.

Familial adenomatous polyposis

Clinically defined as presence of >100 colorectal adenomas.

Over 80% of cases come from patients with a positive family history.

20% arise as a result of new mutations in the adenomatous polyposis coli gene (APC).

It is less common that hereditary non-polyposis colorectal cancer (HNPCC) and accounts for <1% of colorectal cancer (CRC).

Although the large bowel is mainly affected, polyps can occur in the stomach, duodenum and small intestine.

It’s inherited and mendelian dominant conditions.

Risk of CRC is 100% in patients with FAP.

Males and females are equally affected.

It can also occur sporadically without any previous sign or history, presumably by new mutations. There’s often, in these cases, a history of large bowel cancer occurring in young adulthood or middle age, suggesting preexisting adenomatosis.

FAP can be associated with benign mesodermal tumors such as desmoid tumors and osteomas. Epidermoid cysts can also occur (Gardner’s syndrome) ; desmoid tumors in the abdomen invade locally to involved the intestinal mesentery and, although non-metastasising, they can become unresectable.

Up to 50 per cent of patients with FAP have congenital hypertrophy of the retinal pigment epithelium (CHRPE), which can be used to screen affected families if genetic testing is unavailable.

Clinical features

Polyps are usually visible on sigmoidoscopy by the age of 15 years and will almost always be visible by the age of 30 years.

Carcinoma of the large bowel occurs 10–20 years after the onset of the polyposis.

One or more cancers will already be present in two-thirds of those patients presenting with symptoms at the time of diagnosis

Symptomatic patients

Are either patients in whom a new mutation has occurred or those from an affected family who have not been screened.

They may have

  • Loose stools
  • Lower abdominal pain
  • Weight loss
  • Diarrhoea
  • Passage of blood and mucus

Colonoscopy is performed with biopsies to establish the number and histological type of polyps.

If over 100 adenomas are present, the diagnosis can be made confidently.

If there are no adenomas by the age of 30 years, FAP is unlikely. If the diagnosis is made during adolescence, operation is usually deferred to the age of 17 or 18 years unless symptoms develop.

Screening policy

  • At-risk family members are offered genetic testing in their early teens.
  • At-risk members of the family should be examined at the age of 10–12 years, repeated every year.
  • Most of those who are going to get polyps will have them at 20 years, and these require operation.
  • If there are no polyps at 20 years, continue with yearly examination until age 50 years; if there are still no polyps, there is probably no inherited gene.

Carcinomatous change may exceptionally occur before the age of 20 years. Examination of blood relatives, including cousins, nephews and nieces, is essential, and a family tree should be constructed and a register of affected families maintained.

Treatment

The aim of surgery is to prevent the development of colorectal cancer. The surgical options are:

  • colectomy with ileorectal anastomosis (IRA);
  • restorative proctocolectomy (RPC) with an ileal pouch-anal anastomosis, the anastomosis may be defunctioned with a loop ileostomy;
  • total proctectomy and end ileostomy (normally reserved for patients with a low rectal cancer).

The patient is almost always young and likely to prefer to avoid a permanent stoma and so the choice is normally between the rst two options.

The advantage of an IRA is that

  • it avoids the temporary stoma frequently required for an RPC
  • avoids the potential compromise to sexual function that accompanies proctectomy.
  • has a lower morbidity and mortality.

However, the rectum is left and requires regular surveillance, as there is a risk of adenomas and carcinomas in the residual large bowel. Even with optimal surveillance of the rectal remnant, up to 10 per cent will develop invasive malignancy within a 30-year follow-up period.

Restorative proctocolectomy has the advantage of removing the whole colon and rectum (although a small cuff of rectal mucosa may be left behind with a stapled anastomosis). However, there is a pouch failure rate of about 10 per cent. In addition, and particularly where a stapled anastomosis has been created, there remains a very small but denite incidence of cancer developing in the small strip of rectal mucosa between the pouch and the dentate line. This is why some colorectal surgeons advocate complete mucosectomy of the residual rectal cuff and a transanal pouch anal anastomosis, although it is acknowledged that this results in worse function.

Postoperative surveillance

  • rectal/pouch surveillance, with biopsy of the pouch-anal anastomosis.
  • Gastroscopies are also carried out to detect upper gastrointestinal tumours.

Even with prevention of colorectal cancer, FAP patients have reduced life span due to the development of duodenal and ampullary cancers and the complications of desmoid tumours.

Hereditary non-polyposis colorectal cancer (Lynch syndrome)

characterised by increased risk of colorectal cancer and also cancers of the endometrium, ovary, stomach and small intestines.

It is an autosomal dominant condition that is caused by a mutation in one of the DNA mismatch repair genes. The most commonly affected genes are MLH1 and MSH2.

The lifetime risk of developing colorectal cancer in Lynch syndrome is 80 per cent, and the mean age of diagnosis is 45 years.

Most cancers develop in the proximal colon.

Females with HNPCC have a 30–50 per cent lifetime risk of developing endometrial cancer.

Diagnosis

Tumours of the large intestine 1163 HNPCC can be diagnosed by genetic testing or the Amsterdam II criteria:

  • three or more family members with an HNPCC-related cancer (colorectal, endometrial, small bowel, ureter, renal pelvis), one of whom is a rst-degree relative of the other two;
  • two successive affected generations;
  • at least one colorectal cancer diagnosed before the age of 50 years;
  • FAP excluded;
  • tumours veried by pathological examination.

Patients with HNPCC are subjected to regular (every one to two years) colonoscopic surveillance.

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