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Need to know: colorectal cancer

Cancer expert Professor Bob Steele answers burning questions from GP Dr Colin Kenny

1. How can colorectal cancer be prevented?

Do aspirin or NSAIDs have any part to play?

The precise lifestyle alterations required to minimise the risk of bowel cancer are not known but the key preventive behaviour is to increase exercise and avoid weight gain. There is some evidence that fibre and vegetables may be protective and some rather weaker evidence that red meat may be a risk factor. There is certainly good evidence from epidemiological studies that aspirin and, to a lesser extent, other NSAIDs, are associated with decreased risk of bowel cancer.

However, given the increased risk of gastric ulceration and bleeding associated with chronic aspirin intake, there is still no good evidence to support its routine use. Of course, it must also be appreciated that colonoscopy and removal of adenomas can prevent bowel cancer and it is perhaps not widely appreciated that screening using faecal occult blood testing or flexible sigmoidoscopy detects adenomas as well as cancers and thus actually prevent bowel cancer.

2. At what age and with what family history should patients be offered screening? Should this be colonoscopy or faecal occult bloods – or both? Is there a place for spiral CT scans?

Individuals with three family members affected by bowel cancer are advised to undergo colonoscopy every two years from the age of 30 to 70. Likewise those known to carry the HNPCC gene should have similar screening. Individuals with one first-degree relative affected by bowel cancer when aged 45 years or under, or people with two affected first-degree relatives, should have a colonoscopy at the age of 30 to 35 and a repeat examination at age 55.

It should be noted that people with a significant family history of bowel cancer are at reasonably high risk and therefore should have colonoscopy and not faecal occult blood testing, which is insufficiently sensitive. It is possible, however, that CT colography (imaging of the colon reconstructed from a spiral CT scan taken with full bowel preparation and insufflation of the colon with air) could replace colonoscopy in these people, although there is as yet no firm evidence to support this approach.

3. When considering the risk of bowel cancer, which symptoms – such as age, weight loss, per rectum bleeding – help to stratify the risk of the presentation being bowel cancer?

The main alarm symptoms are:

• rectal bleeding with a change in bowel habit to looseness or increased frequency

• rectal bleeding without anal symptoms in any patient over 50

If these symptoms persist over a period of six weeks such a patient should be urgently investigated. In addition, any patient with a palpable abdominal or rectal mass or intestinal obstruction should, of course, be investigated on an urgent basis. It should also be noted that patients with iron deficiency anaemia (Hb <11g l="" in="" men="" or=""><10g l="" in="" post="" menopausal="" women)="" without="" overt="" cause="" should="" be="" thoroughly="">

4. What type of blood loss is the most worrying for bowel cancer?

Bright red rectal bleeding that occurs at the end of defecation and tends to drip into the toilet pan is highly suggestive of haemorrhoids and is unlikely to be associated with bowel cancer. The most worrying type of rectal bleeding is that associated with increased looseness of stool but any blood seen mixed with the stool or coating the surface of the stool should prompt investigation.

5. What are the most common sites on the bowel for cancer and what are the most common types?

The most common site is the rectum followed by the sigmoid colon. Some 75 per cent of cancers will be found in this region. A further 10 per cent are found in the caecum and the rest are fairly evenly distributed throughout the colon. By far the most common type of cancer is adenocarcinoma and the prognosis is largely determined by the stage of the tumour (see question 7).

The only other type of cancer affecting the large bowel with any frequency is squamous carcinoma of the anal canal. If detected early, this has a relatively good prognosis and is now primarily treated by a combination of radiotherapy and chemotherapy, although some will require abdominoperineal excision of rectum if this fails.

6. If bowel cancer is diagnosed, when is a colostomy inevitable? Is interval colostomy with reconnection now less common?

A colostomy is inevitable when a carcinoma of rectum extends down to the anal sphincters; it is essential to remove the rectum and anal canal and the patient will have a

permanent colostomy (abdominoperineal excision of rectum). In general, this procedure is usual in patients with cancer of the lower third of the rectum. Improvements in technique now make it possible to form an anastomosis after resection of tumours of the upper two thirds of the rectum.

In good centres, rectal cancers requiring a permanent colostomy should be no more than 30 per cent. Interval colostomy with reconnection used to be a standard procedure for patients presenting with obstructing cancer of the rectum or sigmoid colon. But now there is a move towards using expanding metal stents inserted radiologically to overcome obstruction, and patients treated in this way can then go on to have elective colectomy without the need for an interval colostomy.

7. How does the site and pathology of the tumour stratify the chances of cure and risk of recurrence?

Tumours of the colon and rectum are classified in various ways but the most commonly used is the Dukes classification. When a tumour is removed and sent to the pathology department the extent of invasion through the bowel wall is measured and the draining lymph nodes are examined for metastases.

If the muscular wall of the colon has not been penetrated and there are no lymph nodes involved, this is a stage A tumour and the five-year survival is about 90 per cent. If the bowel wall has been penetrated but there are still no lymph nodes involved, this is a stage B tumour, and the five-year survival is roughly 60 per cent.

If, however, lymph nodes have become involved, this is a stage C tumour and only 30 per cent of such patients will survive five years. Stage for stage, the site within the colon seems to have little effect on prognosis and risk of recurrence, although very low rectal cancers requiring an abdominoperineal excision of rectum tend to recur more readily than other tumours.

8. What problems may be expected from patients with a colostomy who intend to fly?

The only real problem such patients might expect to encounter is increased production of gas by the colostomy in the relatively depressurised atmosphere of the plane cabin. This will cause the bag to swell and under extreme circumstances may cause it to pop off. The patient should avoid eating a lot of green vegetables, pulses or beans before flying.

9. Chemotherapy is now more commonly used in bowel cancer. Should it be used routinely after surgery to improve the cure rate? Is palliative chemotherapy useful and acceptable?

It is now generally agreed that all patients with a Dukes' stage C cancer (see question 7) should be offered chemotherapy after surgery as this improves the chances of long-term survival by between 5 and 10 per cent. But in many elderly patients, the toxicity of chemotherapy outweighs any advantage and this type of treatment tends to be reserved for younger patients.

The evidence that chemotherapy is of any advantage in Dukes' stage B tumours is less convincing although many oncologists will use it, particularly if there is a tumour seen in blood vessels outside the colon by the pathologist. It is generally agreed that patients with Dukes' stage A cancers do not require chemotherapy.

Palliative chemotherapy for patients with advanced disease is increasingly effective, although there is still no prospect of cure from chemotherapy alone for metastatic bowel cancer. It has to be said, however, that the median survival advantage is still modest at little more than one year. Yet there is good evidence that this extra year is associated with good quality of life.

10. Increasingly I have seen chemotherapy used for liver metastases. How much does this add to survival? I have also seen liver metastases resected – how much benefit can be expected?

Patients with liver metastases treated with chemotherapy alone might be expected to live for an extra year with a reasonable quality of life, as mentioned above. Resection of part of the liver for liver metastases is effective and can produce five-year survival rates of up to 30 per cent (very similar to that seen in Dukes' stage C primary cancers). Unfortunately, only a relatively small proportion of patients who develop liver metastases are suitable for this. More recently, a technique called in situ ablation – where radio frequency or cryotherapy probes are used to destroy liver metastases – has been introduced. Although the benefit is not as clear as for resection of limited liver metastases, it does appear to prolong life to a certain extent.

11. When is radiotherapy considered useful in the management of bowel cancer?

It is generally agreed among radiation oncologists that radiotherapy should not be used for colon cancer as damage to the surrounding organs, particularly the small bowel, is likely to lead to major morbidity.

However, there is increasing evidence that radiotherapy used in conjunction with surgery for rectal cancer reduces local recurrence rates and improves survival.

It is now established that radiotherapy before surgery is more effective and is associated with less morbidity than radiotherapy after resection. There is, however, still debate as to exactly which patients should receive radiotherapy. Perhaps the most useful indication for pre-operative radiotherapy is the situation in which the surgeon cannot be absolutely sure of being able to remove the entire tumour with a good margin of normal tissue by surgery alone.

Bob Steele is professor of surgery and head of the department of surgery and molecular oncology at Ninewells Hospital and Medical School, University of Dundee. He is director of the Scottish Colorectal Cancer Screening Pilot and chairs SIGN's Colorectal Cancer Focus Group and the NICE Colorectal Cancer Guidance Group

Competing interests None declared

What I will do now

Dr Kenny responds to the answers to his questions

• I will encourage patients to prevent bowel cancer by increasing exercise, avoiding weight gain and using aspirin carefully, taking into consideration the risks of GI bleeding

• I will also take a careful history – knowledge of degree of relatives and their age of developing bowel cancer is needed before patients are referred for colonoscopy

• I intend to regard rectal bleeding, especially where the blood is mixed

with the stool, as an important alarm symptom for bowel cancer, especially if the patient is over 50 and has no anal symptoms

• I will now counsel the patient that they will need a colostomy when a carcinoma of rectum extends down to the anal sphincters but new techniques may prevent interval colostomies

• From now on I will Inform patients that tumour staging, and the patient's age and physical state, govern whether the patient will need chemotherapy after surgery

Colin Kenny is a GP in Dromore, Co Down

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