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Assessing patients for risk of colorectal cancer in primary care

Every year there are around 35,000 new cases of colorectal carcinoma (CRC)

diagnosed in the UK.1 Bowel cancer was responsible for more than 16,000 deaths in the UK in 2004, making it the second largest cause of cancer death.2

Although the overall five-year survival rate has improved, it remains below 50

per cent. The stage at which bowel cancer is diagnosed is the most important determinant of outcome.

Risk Factors

There is conflicting evidence as to

whether diet affects the incidence of CRC. However, a high-fibre diet rich in fruit and vegetables with limited red meat is thought to be protective.3

HRT has a protective effect (reducing the absolute risk by six per 10,000 women per year),4 but this benefit has to be balanced against the increased risk of other conditions, such as breast cancer.

Although smoking, alcohol, lack of exercise and obesity are associated with an increased risk of CRC,5,6 the most important risk factors are:

• previous colorectal adenoma

• longstanding inflammatory bowel disease

• significant family history

Familial adenomatous polyposis and hereditary non-polyposis CRC?(HNPCC) account for 1 per cent and 2 to 5 per

cent of CRC cases respectively. The background lifetime risk for CRC is 1 in 45.

Table 1?(see page 8) details the current Scottish Cancer Group criteria for screening, recommended by the SIGN guideline on colorectal cancer.6

Signs and symptoms

Symptoms arising from the GI tract are extremely common in the community and many patients with these symptoms do not present to doctors.

Changes in bowel habit and abdominal pain are more common than rectal bleeding. Studies have suggested that

18 to 19 per cent of the population experience rectal bleeding per year, however these studies used postal questionnaires and only 60 to 70 per cent of those polled replied.7,8

The challenge for GPs is to identify those patients most likely to have CRC, as significant risks are associated with both under- and overinvestigation.9

The classic symptoms associated with colorectal carcinoma are:

• Rectal bleeding

• Change in bowel habit

• Weight loss

• Abdominal pain

There have been a number of relatively small studies in primary care that demonstrate the importance of rectal bleeding. These have found that 5.7 to

15.5 per cent of patients with new onset rectal bleeding over the age of 40 to 50 have colorectal carcinoma,10-15 although not all patients with rectal bleeding may have been included in these studies, possibly overestimating the positive predictive value.

Rectal bleeding with a change of bowel habit to a looser stool16 and/or weight loss,17 and absence of anal symptoms,16 is associated with an increased risk of colorectal carcinoma. There is conflicting evidence from primary care studies as to whether dark rectal bleeding or blood mixed in a stool are more likely with CRC.16,18,19

Predictive signs of CRC are:

• Anaemia

• A right side abdominal mass

• A rectal mass on digital rectal examination

In the case of advanced CRC, a patient may present with large bowel obstruction or the symptoms and signs of metastatic disease. The most common site for CRC metastases is the liver.

National guidance

In 2000, the Department of Health introduced referral guidelines to help GPs identify patients with suspected cancer who needed to be seen urgently by a specialist under the two-week rule. The guidance was based on data from both primary and secondary care. It divided patients into two groups; those at high risk and those at low risk of having CRC.20

A policy of ‘safe, watchful waiting', dependent on patients understanding and accepting the level of risk, has been advocated for those in the low-risk group.9 It has been recommended that patients with symptoms for longer than three months should still be referred


The aim of the DH guidelines was to capture 90 per cent of those with CRC as urgent referrals without overwhelming hospital services. Unfortunately, only up to 50 per cent of patients with CRC present at rapid access clinics, and those referred under the two-week rule have more advanced disease.21,22 It may be that not all patients fulfilling the criteria are being referred or that the criteria miss a significant number of patients. In 2005 the DH?guidelines were replaced by the NICE?referral guidelines for suspected cancer (see table 2, left).23

The NICE?guidelines include a ‘treat, watch and wait' period as an option in patients with equivocal symptoms. The need for digital rectal examination in patients with unexplained gastrointestinal tract symptoms is emphasised. The risk factors of ulcerative colitis and family history of colorectal cancer are considered.

The SIGN guidelines, published in 2003, advocate a lower age limit of 50 years for investigation when age is a criterion for referral.6 An argument for referral can be made for all patients presenting with new onset rectal bleeding over the age of 50, even if they have a local cause such as haemorrhoids. Referral can be non-urgent in the absence of other high-risk features.


Screening for colorectal cancer using faecal occult bloods (FOB) has been shown to reduce mortality by

16 per cent.24

In July 2006 the NHS Bowel Cancer Screening Programme started in England, and will be rolled out across the whole country during the next three years. Scotland will start a screening programme in 2007.

The screening programme is administered by screening centres. Men and women aged 60 to 69 years (50 to

74 years in Scotland) will be offered screening every two years. They will receive a letter and leaflet explaining the programme and how to take the samples, followed by an FOB kit one week later.

Six samples are collected from three separate bowel motions. Patients will be notified of the result within two weeks of their samples arriving at a testing centre. It is anticipated that 2 per cent of tests will be abnormal and 4 per cent unclear (the majority of which will be normal when repeated).

The screening centres will provide colonoscopy for those with abnormal results, and will be responsible for referring those requiring treatment to local hospitals. At colonoscopy about

50 per cent of patients will have normal findings, 40 per cent will have polyps and

10 per cent will have cancer.

GPs will not be involved, although they will be informed when screening is taking place in their area.


Lower gastrointestinal symptoms may be investigated by barium enema (preceded by rigid sigmoidoscopy if rectal bleeding is present), flexible sigmoidoscopy

(for rectal bleeding in the absence of other features), or colonoscopy.

Colonoscopy is more sensitive for CRC than barium enema (95 per cent compared with 82.9 per cent).25 It allows for lesions to be biopsied or removed, and detects more Dukes' stage A carcinomas than barium enema.

Following diagnosis, ultrasonography is often used to screen for liver metastases. CT scans are performed to determine the local invasion of large tumours and to assess the pelvis in the case of rectal tumours.

Virtual colonoscopy involves a CT

scan and 3D image reconstruction of

the colon. Virtual colonoscopy has been found to be comparable with colonoscopy in detecting colorectal polyps in asymptomatic adults.26 However, it gives

a large radiation dose, and its place in screening has not been clarified.


CRC is an important cause of morbidity and mortality in the UK. Assessment of risk is essential to avoid overwhelming hospital services with inappropriate referrals. The development of computer generated risk scores may help to prioritise patients more accurately.27

Although the five-year survival rate

has improved slightly over recent years,

it may be that screening for CRC, and

the consequent diagnosis of

pre-symptomatic early colorectal cancer and the removal of pre-cancerous adenomatous polyps, will provide the most successful way of reducing mortality further.


1 UK Bowel Cancer incidence statistics.

incidence/ 2006. 12-9-2006

2 Atkin WS. Impending or pending? The national bowel cancer screening programme. BMJ 2006; 332:742

3 COMA. Nutritional Aspects of the Development of Cancer. 1998. London, Department of Health

4 Rossouw J, Anderson GL, Prentice RL?et al. Risks and benefits of estrogen plus progestin in healthy postmenopausal women: principal results from the Women's Health Initiative randomized controlled trial. JAMA 2002;288(3):321-33

5 Bowel cancer risk factors.

riskfactors/ 2005. 18-9-2006

6 Scottish Intercollegiate Guideline Network. SIGN?67: Management of Colorectal Cancer: a national clinical guideline. 2003

7 Crosland A, Jones R. Rectal bleeding: prevalence and consultation behaviour. BMJ 1995;311:486-8

8 Thompson MR, Pond?CR, Ellis BG et al. Rectal bleeding in general and hospital practice; 'the tip of the iceberg'. Colorectal Dis 2000;2:288-93

9 Thompson MR, Heath I, Ellis BG, et al. Identifying and managing patients at low risk of bowel cancer in general practice. BMJ 2003;327:263-5

10 Goulston K, Dent O. How important is rectal bleeding in the diagnosis of bowel cancer or polyps? Lancet 1986;2;261-5

11 du Toit J, Hamilton W, Barraclough K. Risk in primary care of colorectal cancer from new onset rectal bleeding: 10 year prospective study. BMJ


12 Fijten G, Muris GW, Starmans R et al. The incidence and Outcome of Rectal Bleeding in General Practice. Fam Pract 1993;10:283-7

13 Metcalf J, Smith J, Jones R, et al. Incidence and causes of rectal bleeding in general practice as detected by colonoscopy. Br J Gen Pract 1996;46:161-4

14 Norrelund N, Norrelund H. Colorectal cancer and polyps in patients aged 40 years and over who consult a GP with rectal bleeding. Fam Pract 1996;13:160-5

15 Wauters H, Van Casteren V, Buntinx F. Rectal bleeding and colorectal cancer in general practice: diagnostic study. BMJ 2000;321:998-9

16 Ellis B, Thompson M. Factors identifying higher risk rectal bleeding in general practice. Br J Gen Pract 2005;55:949-55

17 Hamilton W, Round A, Sharp D, et al. Clinical

features of colorectal cancer before diagnosis: a population-based case-control study. Br J Cancer 2005;93:399-405

18 Fijten G, Starmans R, Muris?GW et al. Predictive value of signs and symptoms for colorectal cancer in patients with rectal bleeding in general practice. Fam Pract 1995;12:279-87

19 Mant A, Bokey E, Pierre H, et al. Rectal bleeding. Do Other Symptoms Aid in Diagnosis? Dis Col Rectum 1989;32:191-6

20 DOH. Referral guidelines for suspected cancer. 2000. 18-9-2006

21 Flashman K, O'Leary D, Senapati A, et al. The Department of Health's "two week standard" for bowel cancer: is it working? Gut 2004;53:387-91

22 Jones R, Rubin G, Hungin P. Is the two week rule for cancer referrals working? BMJ 2001;322:1555-6

23 National Institute for Health and Clinical Excellence (NICE) (2005) Referral guidelines for suspected cancer (Clinical Guideline 27). London: NICE. Available from

24 Towler BP, Irwig L, Glasziou P, et al. Screening for colorectal cancer using the faecal occult blood test, Hemoccult. Cochrane Database of Systematic Reviews 1998;2:CD001216

25 Rex DK, Rahmani EY, Haseman JH, et al. Relative Sensitivity of Colonoscopy and Barium Enema for Detection of Colorectal Cancer in Clinical Practice. Gastroenterology 1997;112:17-23

26 Pickhardt P, Choi JR, Hwang?I, et al. Computerised tomographic virtual colonoscopy to screen for colorectal neoplasia in asymptomatic adults.

N Engl J Med 2003;349:2191-200

27 Selvachandran S, Hodder R, Ballal M, et al. Prediction of colorectal cancer by a patient consultation questionnaire and scoring system: a prospective study. Lancet 2002;360:278-83

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