Cancer of the colon and rectum

Abstract

In lieu of an abstract, here is a brief excerpt of the content: •104• Chapter 10 Cancer of the Colon and Rectum S.B. Naaeder and J.C.B. Dakubo Introduction Population and epidemiological studies have established a marked variation in the incidence of colorectal cancer in different parts of the world. The disease is common in Western societies when compared with its incidence in developing countries in Africa, Asia and South America. The apparently low incidence of colon and rectal cancer in Africa, may be due to the enormous scourge from communicable diseases and malnutrition that had kept down life expectancy in the African as well as the lack of accurate cancer records. Colorectal cancer is a disease of older persons and therefore as a population grows older the incidence of the disease will increase on demographic grounds alone. Such increase in the average life expectancy and the incidence of colorectal cancer in some populations in Africa has been reported1 . However, major demography- linked increases in the colorectal cancer burden in developing countries may not take place for some time because young persons will continue to form the majority of the population. Incidence The worldwide incidence of colorectal cancer now exceeds 1.2 million index cases per year, half of whom will die of their disease2 . Globally, colorectal cancer is the third commonest malignant neoplasm after cancer of the lung and breast (women only). It retains its third position after lung and prostate cancer in men and rises to become the second most common cancer after breast cancer in women. It accounts for 10.0 percent of all malignant neoplasms in males and 9.4 percent of all malignant tumours in females worldwide.2 It is slightly more common in men than in women (ratio 1.4:1).2 The incidence •105• Cancer of the Colon and Rectum is highest in Australia/New Zealand, Western Europe and North America and lowest in South America, South-Central Asia, the Middle East and Africa. Intermediate rates are noted in Eastern Europe, Latin America and parts of Asia as well as Southern Africa. Currently the incidence rates are stabilizing in Northern and Western Europe. In the USA colorectal cancer incidence has been declining in the past two decades, largely due to screening of asymptomatic individuals and removal of colorectal polyps before they progress to cancer3 . However, the incidence of colorectal cancer is increasing in developing countries which now contribute a little over a third of new cases of colorectal cancers to the annual worldwide incidence2 . In West Africa the incidence of colorectal is increasing, albeit, slowly. Generally, incidence rates change with time. In Ghana there has been an 8-fold increase in the number of new cases of colorectal cancer seen per year from an average of 4.1 new cases in the 1960s to an average of 32.6 new cases currently4,5 . It is now the third most common malignant disease after cancer of the breast and liver in Ghana6 . In Nigeria it is the fourth most common malignant neoplasm7 . Hospital-based data in Ghana and Nigeria show the crude incidence rates of colorectal cancer to be 11.18 per 100 000 population and 3.4 per 100 000 population respectively.5,7 These rates are far lower than the incidence rates of over 40 per 100 000 population reported in Western nations.8 Cancer of the colon and rectum is one of the leading causes of death from malignant disease. It is the fourth most frequent cause of cancer death worldwide accounting for 8.0 percent of cancer deaths.2 In the USA colorectal cancer ranks third as a cause of cancer death after lung and prostate cancer in men and after lung and breast cancer in women3 . Whereas the mortality rate from colon cancer is decreasing in the United States and Western Europe the opposite is occurring in Central and Eastern Europe and lowest in Africa.2,8 In Ghana it is the 10th cause of cancer death overall and the 8th and 9th cause of cancer deaths in males and females respectively.9 Risk Factors A number of risk factors are associated with colorectal cancer, some modifiable and others non-modifiable. The non-modifiable risk •106• Chapter 10 factors include age, sex and genetic factors. Cancer of the colon and rectum affects all age groups but the risk increases with age with a little over 90 percent of cases aged 50 years or older in western countries.3 In 1960 6.7 percent of Ghanaians were 50...