Colorectal Cancer

Epidemiology of Cancers: Colorectal Cancer

Description
More than 90% of cases are adenocarcinomas and the majority of these arise from adenomatous polyps (established precursors for colorectal cancer)¹.

These common benign tumours develop from normal colonic mucosa and are present in about one-third of the European and US populations ^1,2.

Flat adenomas (more difficult to detect) account for about 10% or all lesions and may have a greater propensity to malignant change².

Only a small proportion of polyps (1-10%) develop into invasive cancer. Indicators for progression from adenomas to invasive cancer include large size, villous histology and severe dysplasia.

Symptoms

• Symptoms vary with the site of the tumour and may be absent in early disease.
• The presenting features of colon cancer are often non-specific, such as weight loss and anaemia due to occult blood loss.
• Rectal and distal colon cancers, on the other hand, usually present with bleeding and/or altered bowel habits, a fifth of patients may present with acute bowel obstruction or peritonitis.

Epidemiology

• Worldwide an estimated 1 million cases of colorectal cancer occur each year, accounting for more than 9% of all new cancers. Colorectal cancer is the fourth commonest form of cancer occurring worldwide.
• Significant variation in colorectal cancer incidence exists between countries, with rates varying 20 fold between countries. The highest rates are observed in Europe. North America and Japan and the lowest rates in Asia and Africa¹.

Age standardized (world) incidence rates by sex for selected countries: 2001 estimates

Source: Cancer Research UK.

• Incidence increases significantly with age, with more than 90% of cases occurring in persons aged 50 years and older.
• The incidence in men and women are similar until age 40 after which a higher incidence is observed among men.
• In 2002 there were 34,889 new cases of large bowel cancer in the UK (63% in the colon and 37% in the rectum)².
• Increases in the incidence in colorectal cancer have been reported in many countries including Eastern Europe and in Britain, where male incidence rates have increased by an average of 0.5% each year for the last 20 years (particularly in men aged 70-79).
• Increases in the incidence of colorectal cancer have also been observed in Japan and may reflect an increase in the consumption of meat and dairy products which increased 10 fold between the 1950s and 1990s².
• Studies for colorectal cancer in migrants has shown incidence rates may rapidly reach those of the host country suggesting a significant influence of dietary and environmental factors on the risk of colorectal cancer¹.
• Colorectal cancer is the second most common cause of cancer deaths in the UK. In  2004 there were 16,148 death from colorectal cancer. Of these 10,318 were deaths from colon cancer and 5,830 from rectal cancer².
• Worldwide colorectal cancer kills approximately 529,000 people each year, with around 60% of these occurring in developed countries. Mortality rates are highest in Eastern European countries such as the Czech Republic and Hungry and the lowest in African and Asian countries².
• Improvements in five-year survival from colorectal cancer have been observed over the last 30 years, due to earlier detection and improvements in treatment.

Risk Factors

• Age -  85% of cases occur in individual aged >60
• Family history - having a first degree relative with colorectal cancer approximately doubles risk.
• Diet - that is high in fat, red meat, smoked foods, nitrosamines, alcohol and low in vegetables, fruit, folate, fibre, B12, B6 and calcium may increase risk of colorectal cancer.
• Obesity
• A history of ulcerative colitis
• A history of polyposis coli

Screening and Prevention
The aim of colorectal cancer screening is to identify precancerous polyps, abnormal growths in the colon or rectum so that they can be removed before they develop into cancer. Screening also helps identify colorectal cancer early. When found early and treated the 5-years relative survival rate is 90%.

Colorectal cancer is a good candidate for population based screening. It is relatively common, most cases develop slowly over years, there are acceptable screening tests and early intervention can be cost-effective and result in better outcomes and decreased mortality².

Several tests can be used alone or in combination to screen for colorectal cancers.

Faecal occult blood test (FOBT) -  Tests for occult blood in stool. Shown to reduce mortality but not incidence. Cost effective.

Flexible sigmoidoscopy - looks for adenomas in the rectum and sigmoid colon before they progress to cancer.

Colonoscopy -  Similar to sigmoidoscopy, except that the tube used is longer and allows examination of the entire colon. More expensive and not considered to be appropriate for mass population screening in the UK².

In the UK,  a national bowel cancer screening programme based on FOBT will be phased in from 2006 for men and women aged 60-69 who will be invited for screening every two years. It is predicted that deaths from bowel cancer could drop by 15%and save an estimated 1,200 lives each year.

References

1. Adami, HO, Hunter D, Trichopoulos D, eds. Textbook of Cancer Epidemiology, Oxford University Press: New York, 2002.
    
2. Cancer Research UK: http://info.cancerresearchuk.org:8000/cancerstats/

© CM Kirwan 2006