The cause of cancer in the intestine is unknown despite extensive and continuing research.

Patients with Crohn's disease of the small and/or large intestine have an increased risk of developing cancer at these sites.

Most patients never develop cancer, but its early detection in patients at increased risk can lead to prompt and curative treatment. The risk should therefore not cause you great concern because if you have had extensive disease for 10 years or more, you will be offered regular screening and monitored very closely.

The risk is related to 2 main factors:
1. The duration of inflammation, (i.e. the length of time since it was first diagnosed).
2. The site and severity of the disease.

There appears to be some evidence that it occurs more frequently in chronically active disease than it does in previously active or intermittent disease.

Duration
Studies have shown that the chance of developing cancer of the colon rises steadily in all patients with the length of time the disease has been present.

Several studies have been carried out to estimate the risk by following patients over a period of 10-40 years. Some failed to show an associated risk, but others predicted an increase which was twice that of the general population for developing colorectal cancer. If the disease is confined to the colon (large intestine), this risk is estimated at around 5 times greater.

The risk of small intestinal cancer has been estimated at around 6 times that of the general population, but as this is an extremely rare cancer in the general population, the risk in Crohn's disease is still small.

(The above figures are only estimates and may vary among different studies according to referral centres and selection biases).

The site and severity of the disease
Cancers of the small intestine in Crohn's disease tend to occur in areas affected by underlying inflammation. Most small intestinal tumours occur in the terminal ileum when severe inflammation, with consequent narrowing and stricture formation, has persisted.

Cancer of the large intestine tends to occur when the right side of the colon is affected with associated strictures and/or fistulous disease.

Cancer may also be associated with long-standing perianal disease (ano-rectal fistulae, fissures, abscesses) which has not responded to conventional treatment.

What are the signs and symptoms?
These may be variable according to the site and extent of the cancer, but mostly show a general worsening of the symptoms associated with the disease:
1. Increasing abdominal/perianal pain.
2. Change in bowel habit:
• constipation (may signify small bowel obstruction).
• diarrhoea with urgency and incontinence (possible rectal lesion).
• blood in the motions.
3. Anorexia (poor appetite).
4. Faeculant discharge.
5. Vomiting (may signify small bowel obstruction).

Late symptoms may include:
- weight loss
- fatigue (probably due to anaemia)
- general deterioration in health

After 10 years of disease, particularly in the colon, such symptoms should be taken seriously and discussed with your doctor.

How may it be detected?
As you approach the risk period, (i.e. 10 years of extensive disease), your doctor will monitor you very closely for any changes. The type of monitoring will vary according to disease site:

1. Small bowel disease
Long-standing cases of small bowel disease, with chronic stricturing, which deteriorate should be treated surgically at an early stage, particularly if there is any failure of medical treatment.

2. Large bowel disease (unresected)
a) With anal disease
Careful digital examination and sigmoidoscopy will be offered every 6-12 months

b) Without anal disease
If strictures are present a yearly colonoscopy will be offered with brushing and biopsying of the strictures.

If there are no strictures present a colonoscopy and multiple biopsies will be offered on a two-yearly basis.

What happens if cancer is detected?
If cancer is detected or a stricture appears highly suspicious, an operation will be necessary to remove it. This would usually involve cutting out (resecting) the affected area and rejoining the healthy bowel (anastomosis). Although the cancer, or the risk of it developing in that area, is removed, it does not provide a cure for the Crohn's disease. However, with careful post-operative management, relapses can be prevented.

For severe, refractory (not responsive to treatment) perianal disease, removal of the colon (colectomy) and formation of an ileostomy may be indicated. A well-functioning ielostomy with appropriate support from stoma care nurses may be liberating from the misery of persistent fistulae, abscesses or pain and, thus, improve general quality of life. The fear of colorectal cancer is also removed.