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D M Parkin Stomach cancer is the most important cancer in the Asia Pacific region followed by lung, liver, and colorectal cancers (figure 1). Breast cancer and cervix cancer are dominant among women. Stomach Cancer Stomach cancer is a serious problem in China, Japan, Korea, and Central Asia. However, this is a relatively rare tumour in India, Pakistan, and Southeast Asia (including Thailand). Migrant studies show that this is not due to genetics since the incidence declines dramatically within 2 generations for Japanese who immigrate to Hawaii (figure 2). This result indicates that the high rate of stomach cancer in certain populations is due to diet and lifestyle, with salty, smoked, and starchy foods increasing the risk. Eating large amounts of chillies and spicy foods is also thought to elevate the risk of stomach cancer.1 However, low rates are seen in India and Thailand, where the spiciest foods are eaten; it could be that fresh fruit, vegetables, and green tea, which have a protective effect, are responsible. Figure 1. Cancer in Asia by Prevalence.
Figure 2. Incidence of stomach cancer in Japanese male migrants to Hawaii.
Helicobacter pylori infection raises the risk of gastric cancer 2-fold. H Pylori infection is common in developing countries, with the majority of people being infected at some time in their lives approximately 50% of stomach cancers in these areas are associated with this bacteria. During the past few decades the incidence of stomach cancer has decreased in most areas of Asia, which may be due to a change in diet, the availability of refrigeration (so that food preservation needs less salting, pickling, and smoking), coupled with a declining prevalence of H pylori. Lung Cancer Lung cancer is predominantly a cancer of developed countries, which is the result of their history of tobacco smoking. In men, 85% of lung cancers in China are related to smoking, with similar percentages seen in Australia (90%) and Japan (85%), while countries where tobacco is not so well-established such as India have lower percentages of lung cancer associated with smoking. Interestingly, Chinese women from Hong Kong, Singapore, and Shanghai have high rates of lung cancer, although it is rare for women to smoke in these areas. Certainly, the rates are somewhat higher than for non-smoking women in the USA.2-4 This may be due in part to environmental smoke and cooking fumes in the house, although more study is required to ascertain the reason for this phenomenon. Populations with long-established tobacco habits such as Australia experienced an epidemic of lung cancer during the 1970s and 1980s, which is now declining. However, the epidemic is at an earlier stage for women and the incidence of lung cancer is increasing. This increasing trend is also seen in countries such as Japan, which have a more recent history of cigarette smoking. Liver Cancer Liver cancer is particularly common in South and East Asia, particularly in China, Japan, Korea, Indonesia, The Philippines, and Papua New Guinea, while India has a low rate of liver cancer, which is reflected by the low rate among Indians living in Singapore. This geographic pattern largely reflects the prevalence of carriers of hepatitis B antigen. Interestingly, hepatitis B is relatively rare in Japan, where a large proportion of liver cancers are related to hepatitis C (table 1). Table 1. Effects of hepatitis B and C viruses (HBV, HCV) on risk of liver cancer5
Immunisation against hepatitis B is a means of primary prevention of liver cancer. Taiwan has now introduced the vaccination programme into the general population, resulting in a dramatic reduction in the incidence of liver cancer in children.6 This is the first formal demonstration of the efficacy of the vaccine in eliminating liver cancer. Colorectal Cancer Colorectal cancer is a cancer of the developed world, and is highly prevalent in Australia, New Zealand, and Japan. Previously, Japan had a low incidence of and mortality from colorectal cancer. However, Japanese immigrants to the USA (Hawaii) have a higher rate of colon cancer than Caucasian Americans, suggesting that any lifestyle protection disappears with lifestyle changes (table 2). Table 2. Environmental factors affecting risk of colorectal cancer
This trend towards higher rates of colorectal cancer is also seen in Asia, along with an increase in consumption of animal products. Jin et al. predict that, as the incidence of stomach cancer decreases, colorectal cancer is likely to become the most common gastrointestinal cancer among females in Shanghai.7 However, in high-risk countries, such as Australia, there is now a decreasing risk, especially in younger generations, probably due to better diet (more fruit and vegetables). Breast Cancer Breast cancer is relatively rare in Asia, but has a high prevalence in Australia and New Zealand. In Asia, it is most prevalent in the Philippines. Epidemiological studies suggest that reproductive factors are involved in breast cancer (table 3). Dietary factors are also involved, with the most important being obesity and calorie intake. These are all factors that are evolving adversely in modern Asian populations. As countries successfully reduce fertility, the risk of breast cancer will be enhanced, and westernisation of diet may have the same effect. Table 3. Factors involved in breast cancer
As shown by studies of Japanese populations immigrating to Hawaii, unhealthy lifestyle changes result in a trend towards higher rates of breast cancer. In addition, the incidence rates in Shanghai, Singapore, and Mumbai are increasing. If these increases in breast cancer rates continue, the projected incidence is expected to double by 2010. Cervical Cancer Cancer of the cervix is important in India, and in parts of Southeast Asia. In recent years, case control studies have shown the importance of human papilloma virus (HPV) in cervical cancer, with at least 90% of cases being due to this virus. The implications of these findings include the importance of vaccines against HPV for primary prevention and integration of HPV detection into screening programmes. Generally, the rates of cervical cancer are declining in Australia, New Zealand, and Japan, partly due to screening programmes and partly due to lifestyle changes. The rate is also declining in Mumbai, Shanghai, and Singapore, although there are no screening programmes in these cities. In Summary Measures to reduce the incidence of cancer morbidity and mortality in Asia include tobacco control since tobacco is responsible for approximately 30% of male cancers. Hepatitis B vaccination could eliminate up to two-thirds of all liver cancers. Early detection of cervical cancer may be helped by HPV vaccination and dietary and lifestyle changes may reduce the incidence of stomach and large bowel cancers. References 1. Gajalakshmi CK, Shanta V. Lifestyle and risk of stomach cancer: a hospital-based case-control study. Int J Epidemiol 1996;25:1146-1153.
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Emerging Cancer Patterns in Asia
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