Although the causes of bowel cancer are not fully understood, possible risk factors may include the following:

• Age/sex

The development of bowel cancer is strongly associated with age, with more than 80% of cases occurring in those aged 60 and over. Men and women have a similar risk of developing bowel cancer up to age 40, but after this rates are higher for men.

• Diet and lifestyle

There is some evidence to suggest that those who rarely exercise, people who are overweight and people who have a diet high in red meat, low in fruit and vegetables and low in fibre are at increased risk of developing bowel cancer.

• Family history

People who have had either one first-degree relatives diagnosed with bowel cancer before the age of 45 or two first-degree relatives diagnosed at any age, have an increased risk of developing bowel cancer. For these individuals, the lifetime risk increases to 16–25% in men and 10–15% in women. Having one first-degree relative diagnosed at over 65 years of age leads to only a slightly increased lifetime risk of developing bowel cancer.

• Genetic conditions

Familial adenomatous polyposis (FAP) accounts for around 1% of cases of bowel cancer. Patients develop hundreds or thousands of polyps in the colon and rectum in their twenties and thirties, and have almost a 100% chance of developing bowel cancer by their forties. Individuals with FAP are usually offered prophylactic colectomy in their teens or twenties. Hereditary non-polyposis colorectal (bowel) cancer (HNPCC) accounts for around 2–5% of cases of bowel cancer. Polyps develop at a younger age and at a greater frequency than in individuals who do not have the disease, but not in such large numbers as in FAP. HNPCC is linked to bowel cancer in younger age groups, and is the cause of around 40% of cases in individuals under 30 years of age.

Over 90% of bowel cancer cases are adenocarcinomas, arising mainly from adenomatous polyps. Adenomatous polyps increase in prevalence with age, and are present in approximately one in four people by the age of 50. Studies suggest that 1–10% of polyps change into invasive cancers. The development of a polyp into a cancer can take more than 10 years, with larger size, villous history and severe dysplasia being important indicators of progression to invasive cancer. Flat adenomas account for 10% of lesions, are harder to detect and may carry a higher risk of malignancy.

Rectal bleeding, a change in bowel habit and anaemia are the most common presenting symptoms of bowel cancer.
Nausea, weight loss, abdominal pain and anorexia may be experienced in more advanced disease.
Individual symptoms may be poor predictors of bowel cancer; however, the use of a combination of signs and symptoms is more sensitive and specific.

The National Institute for Health and Clinical Excellence (NICE) recommends urgent referral for patients:

• Aged ≥ 40 years who report rectal bleeding with a change of bowel habit towards looser stools and/or increased stool frequency persisting for six weeks or more
• Aged ≥ 60 years who report rectal bleeding persisting for six weeks or more without a change in bowel habit and without anal symptoms
• Aged ≥ 60 years who report a change in bowel habit to looser stools and/or more frequent stools persisting for six weeks or more without rectal bleeding
• Of any age with a right lower abdominal mass consistent with involvement of the large bowel
• Of any age with a palpable rectal mass (intraluminal and not pelvic; a pelvic mass outside the bowel would warrant an urgent referral to a urologist or gynaecologist
• Men of any age with unexplained iron deficiency anaemia and a haemoglobin level of ≤ 11g/100 ml
• Women who are non-menstruating with unexplained iron deficiency anaemia and a haemoglobin level of ≤ 10 g/

Four randomised controlled trials (RCTs) of mass screening using the faecal occult blood test (FOBt) have been carried out: one in the UK, one in Denmark, one in the USA and one in Sweden.
These trials demonstrated a reduction in bowel cancer specific mortality in the screened groups, using biennial screening, annual screening or a combination of the two and with follow up periods ranging from 11 to 18 years.
A meta-analysis of these four trials reported a 16% reduction in bowel cancer specific mortality with screening.

• The colonoscopy procedure

You will be given instruction on how to prepare for a colonoscopy prior to your appointment with Dr Kavin. While the procedure may be uncomfortable, it should not be significantly painful. Various levels of sedation are available from light or conscious sedation to full general anaesthesia although this generally isn’t needed. This is simply to make your comfortable. During a colonoscopy the endoscope, which is a thin tube-like instrument, is then inserted into the rectum to view the internal health of the bowel.

• Polyp management

Polyps found during the colonoscopy procedure are usually removed at the same time. If a biopsy or sample of the bowel tissue is taken, patients will be informed immediately after the procedure. If the result confirms a benign biopsy, a results letter will be dispatched within three weeks of the colonoscopy. A diagnosis of cancer will prompt an outpatient appointment with the doctor, who will discuss the result with you face to face.

• Accuracy of colonoscopy

The sensitivity of colonoscopy, ie. the proportion of abnormalities that are detected by colonoscopy, is thought to be greater than 90%. In about 5% of cases, a bowel obstruction or difficulty in negotiating the colonoscope around the bowel may result in the colonoscopy being incomplete;* either a repeat colonoscopy or imaging is offered in such cases.