The term bowel cancer is usually taken to mean cancer of the large bowel or colon. The colon or large intestine starts in the right lower part of the abdomen. This area is called the caecum and is where the small intestine joins the colon. It is also the area that contains the appendix. The colon then moves up to the right upper area of the abdomen, across the top of the stomach and down the left side until reaching the anus. The very last segment of colon into the anus is called the rectum. bowel cancer thus includes the terms colorectal cancer, colonic cancer and rectal cancer.
Cancer of the small intestine is much rarer than colorectal cancer and will not be discussed here. Similarly, anal cancer is treated differently from rectal or bowel cancer.
How common is bowel cancer?
Colorectal or bowel cancer is the third most common malignant cancer in the UK after lung and breast malignancy. Although the third most common malignancy, bowel cancer is the second most frequent cause of cancer death. Around 1:25 or 4% of the UK population will develop bowel cancer at some stage of their lives. This means around 40,000 new cases are diagnosed every year in the UK. As a result, much effort is spent screening and diagnosing bowel cancer at the earliest possible stage when a cure is possible.
Who does bowel cancer affect?
The incidence of bowel cancer increases with age. Most cases (80%) occur in those who are aged over 60 and colorectal cancer is rarer, but certainly not unknown, below the age of 40 years.
What causes bowel cancer?
The exact cause in the vast majority (>90%) of cases of colorectal cancer is unknown. However, a number of different risk factors are known to increase the risk of developing colorectal cancer. These include:-
Much discussion and research has gone in to trying to identify dietary factors that might cause bowel cancer and therefore, by avoiding them, prevent the disease. Western societies tend to eat large amounts of processed fatty foods which appear to confer an increased risk of developing bowel cancer. In less developed countries, with a more vegetarian diet, the number of bowel cancer cases is lower, although fewer people reach older age in these societies. The adoption of a western diet by people born in less developed countries i.e. in migrants seems to increase the chance of developing bowel cancer.
Populations with a high fibre diet tend to have a low risk of bowel cancer. A high intake of fat and meat, particularly smoked meats, are believed to be risk factors for colorectal cancer. Obesity itself may also increase the chance of developing the disease. Excess alcohol, smoking and a sedentary lifestyle are also linked to bowel cancer.
Current advice for minimising bowel cancer risks suggest a diet rich in green or root vegetables with adequate fibre content. Cabbage, broccoli, brussels sprouts and cauliflower are recommended. Limiting red meat, processed fats and alcohol is wise as is maintaining a normal body weight with regular exercise.
It should be remembered that dietary changes may reduce bowel cancer risk in populations but does not guarantee that any one individual will be free of the disease.
Colorectal Cancer is more common in those with a strong family history of the disease. The greater the number of relatives affected, especially close family members (parents, brothers and sisters) at a younger age, the greater the risk. This can be difficult to assess and the construction of a family tree is required before referral to a Clinical Genetics Unit to determine if bowel cancer screening is required.
A number of specific genetic syndromes have been identified that increases the risk of Bowel Cancer.
Lynch Syndrome or Hereditary Non-Polyposis Colorectal Cancer (HNPCC) is the commonest specific genetic disorder associated with Colon Cancer. HNPCC causes approximately 3% of Bowel Cancer cases. HNPCC is unusual in that the Colorectal Cancer is more common on the right side of the colon, often in the caecum. Also the cancer does not arise within one or multiple polyps.
In contrast, in Familial Adenomatous Polyposis (FAP) there are many polyps, with often well over 100 throughout the bowel. These can present even as young as 10 years’ of age. Colorectal Cancer is inevitable in such patients, usually by the age of 30.
Inflammatory bowel disease
Longstanding Inflammatory Bowel Disease, Ulcerative Colitis or Crohn’s Diseaseincreases the chances of Colorectal Cancer. The risk increases with the extent, severity and duration of the disease. The risk is higher if the whole colon is involved, the disease is more active and has been present for >10 years. Regular surveillance colonoscopies are required to detect the early changes associated with an increased risk of colorectal cancer. NICE (The National Institute of Health and Care Excellence) recommends that all patients are offered surveillance after 10 years of having the disease. Thereafter the interval for surveillance is determined by activity of disease and other important risk factors which are outside the scope of this article and the reader is encouraged to link to www.nice.orh.uk/guidance/cg118/chapter/1-Guidance for further information.
Annual Colonoscopies may be needed if the disease started in childhood or is associated with Sclerosing Cholangitis, a liver disease associated with Inflammatory Bowel Disease.
What is the role of polyps in bowel cancer?
Colonic polyps are generally “warty” outgrowths of the mucosal lining of the large bowel. Polyps come in various shapes and sizes. Some may have large stalks like tress or be more like small bushes. Some may be flat with no stalk at all. Polyps can be made up of different cells. Significant polyps are called adenomas. Adenomas are important as they may grow and eventually become malignant. For this reason, adenomas are generally regarded as the forerunner for developing Bowel Cancer. The risk increases with the size of the polyp. Such polyps can be found and removed using a tube inserted via the anus called a colonoscope. Currently, much effort is expended diagnosing and removing polyps, even in those people with no symptoms to try and reduce the future risk of developing colorectal cancers and to improve long term survival.
What are the symptoms of bowel cancer?
Bowel cancer may occur anywhere in the colon but “hotspots” with increased frequency are the rectum, near the anus, the sigmoid colon just above the rectum, and the caecum on the far right side of the bowel.
Symptoms of colon cancer include:-
- Rectal Bleeding: separate from or mixed in with the bowel motions. Rectal bleeding is more common in rectal or sigmoid colon cancers
- Change in bowel habit: an alteration in normal bowel routine can be significant
- Abdominal pain: often colicky in nature and relieved by opening the bowels
- A feeling the bowel is not completely cleared after defecation: usually a symptom of rectal cancer
- Iron deficiency anaemia: Iron deficiency is common but an important cause is persistent but relatively minor bleeding from a colonic cancer. If bleeding occurs slowly from a cancer in the caecum or right side of the bowel, the blood may mix with the motions and not be visible when going to the toilet.
Bowel cancer not infrequently presents as a surgical emergency, usually bowel obstruction, because the cancer has blocked the gut completely. More rarely, a colorectal cancer may cause a perforation and present as a surgical emergency.
How is bowel cancer diagnosed?
The symptoms of colorectal cancer are very non-specific and can be due to a number of other diseases. Few people have an absolutely regular bowel habit, for example. Therefore large numbers of patients need investigating and only a small minority with bowel symptoms will turn out to have colorectal cancer.
The principal investigative method is endoscopic. That is, directly viewing the colon using a flexible tube inserted through the anus. Flexible Sigmoidoscopy looks at only the left side of the bowel. This includes the rectum and sigmoid but not the caecum. This is often performed without sedation and increasingly by Nurse Endoscopists.
Colonoscopy, if successfully completed, examines the entire large bowel around to the caecum on the right side. This usually requires sedation to make the procedure more comfortable. Colonoscopy rarely takes more than 30 minutes to perform. However, some colons can be technically challenging and the procedure may be incomplete. If this occurs, you clinician will recommend an additional test (e.g. a CT virtual colonoscopy- see below) to complete the examination of the remainder of the bowel.
Endoscopic methods allow direct vision of potential causes and also the ability to take pieces of tissue or biopsies to analyse in a laboratory. Polyps can be removed immediately using heat diathermy. For these reasons, Colonoscopy is usually the first investigation. Both Flexible Sigmoidoscopy and Colonoscopy require the bowel to be cleared with strong laxatives or enemas to allow clear views. Patients usually report the bowel preparation is worse than the procedure itself. Barium enema, an x-ray technique where contrast is inserted to the anus, is now rarely used. CT scanning is now performed if Colonoscopy is unsuccessful or the patient is too frail or elderly for a Colonoscopy. Plain CT however does not show small lesions clearly in the bowel.
CT Virtual Colonography (CTVC) – this emerging technique combines oral contrast preparation, intravenous contrast and CT scanning. Images are acquired with patients lying of their back and on their front. The results are very accurate for polyps >6mm, but still not as good as Colonoscopy. If a potential problem is detected on CT or CTVC, a Colonoscopy may still be required to view, biopsy or treat it. A CT scan has the advantage of detecting abnormalities outside the colon if present e.g. kidney disease.
If it’s not bowel cancer, what else could it be?
The symptoms of bowel cancer are not specific. Rectal bleeding may be coming from around the anus, commonly haemorrhoids (piles) or a fissure.
Polyps, rather than cancer, may produce rectal bleeding or iron deficiency anaemia. Inflammatory Bowel Disease, Ulcerative Colitis or Crohn’s frequently produce diarrhoea, anaemia and rectal bleeding.
Change of bowel habit is a feature of most colonic diseases.
Diverticular Disease is almost universal to some degree over the age of 60 and can produce both pain, bleeding and altered bowel habit.
Functional bowel disease or Irritable Bowel Syndrome affects up to 20% of the normal population and can produce symptoms of a change of bowel habit and abdominal pain although not bleeding.
Iron deficiency anaemia has many other potential causes including:-
- Menstrual blood loss
- Poor diet
- Failure to absorb iron, commonly Coeliac Disease
- Bleeding from the stomach or small intestine, for example peptic ulceration or hiatus hernia
- Inflammatory Bowel Disease
- After previous abdominal surgery (especially gastric surgery)
- Ingestion of Aspirin or other anti-inflammatory drugs (also referred to as NSAIDs)
Causes of diarrhoea are numerous. Many are not caused by colonic disease and may be due to medication or drugs for example.
It is clear that potential symptoms of Colorectal Cancer are non-specific and can easily be mimicked by many other conditions.
How is bowel cancer treated?
Once bowel cancer is detected, the objective is to cure the patient. The outlook or prognosis is heavily dependent on whether the cancer is small and confined to the bowel wall or has already spread or metastasised.
Bowel cancer spreads through the bowel wall into the local lymph nodes. Further spread within the abdomen can occur, especially to the liver. Metastases elsewhere, for example to the lungs or bones, are rarer but not unknown.
For this reason, all patients with colorectal cancer are “staged” to look for cancer spread with a CT scan. Patients with rectal cancer will also have an MRI scan. Depending on these results, further tests may be required but are not performed routinely.
A blood test, Carcinoembryonic Antigen (CEA) will also be measured which can help in monitoring treatment.
If the bowel cancer has not spread, the optimal treatment is surgery. In most cases, the tumour is removed and the colon directly joined up again (re-anastomosed) without the need for a stoma or bowel opening onto the abdominal wall. The exact operation performed depends on the site of the cancer. Avoiding a stoma cannot be guaranteed and can be necessary in an emergency situation. However, this may only be temporary and can be reversed later.
The exception is cases involving the very low rectum just inside the anus. At this site, there is not enough space to remove the cancer safely and retain the anal sphincter. In these circumstances, a permanent abdominal stoma is necessary.