Cancer Patterns in Different Racial and Ethnic Groups in Singapore, With Some Reference to Other Asia-Pacific Groups

Singapore is a veritable human laboratory for the study of cancer patterns, with a compact population (3m) on a small island (640 km2). The ethnic distribution indicates that 78% are Chinese, 14% Malays, 7% Indians and 1 % Others. The validity of ethnic distribution remains, with less than 5% of marriages being inter-ethnic even today. Recently, a full analysis of incidence trends over 25 years (1968-1992) was completed. The age-adjusted relative risks confirmed high risk in Chinese for nasopharynx, oesophagus, stomach, colon, rectum, liver and lung. In Indians, high risk sites were mouth and cervix, and in Malays, ovary and non-Hodgkin's lymphoma. Of special interest are the following: (a) sharp increse in female breast cancer, attributed to a strong cohort effect, thus suggesting the role of lifestyle changes and the finding of a likely protective effect of soya bean products; (b) marked increase in colorectal cancer, partially explained by the high meat: vagetable intake ratio and reduced cruciferous vegetable intake in the high risk group; (c) unchanging incidence of nasopharyngeal carcinoma, and the finding of salted and picked vegetables as a risk factor; (d) increasing proportion of adenocarcinomas (50%) of the lung in female Chinese, which cannot be explained by cigarette smoking and remains a research topic. J Epidemiol,1996 ; 6 : S165-S168.


Cancer
Patterns in Different Racial and Ethnic Groups in Singapore, With Some

Reference to Other Asia-Pacific Groups
Lee Hin-Peng Singapore is a veritable human laboratory for the study of cancer patterns, with a compact population (3m) on a small island (640 km2).The ethnic distribution indicates that 78% are Chinese, 14% Malays, 7% Indians and 1 % Others.The validity of ethnic distribution remains, with less than 5% of marriages being inter-ethnic even today.
Recently, a full analysis of incidence trends over 25 years  was completed.The age-adjusted relative risks confirmed high risk in Chinese for nasopharynx, oesophagus, stomach, colon, rectum, liver and lung.In Indians, high risk sites were mouth and cervix, and in Malays, ovary and non-Hodgkin's lymphoma.
Of special interest are the following: (a) sharp increse in female breast cancer, attributed to a strong cohort effect, thus suggesting the role of lifestyle changes and the finding of a likely protective effect of soya bean products; (b) marked increase in colorectal cancer, partially explained by the high meat: vagetable intake ratio and reduced cruciferous vegetable intake in the high risk group; (c) unchanging incidence of nasopharyngeal carcinoma, and the finding of salted and picked vegetables as a risk factor; (d) increasing proportion of adenocarcinomas (50%) of the lung in female Chinese, which cannot be explained by cigarette smoking and remains a research topic.J Epidemiol,1996 ; 6 : S165-S168.cancer, ethnic groups, Singapore The Asia-Pacific region is one of great diversity.It has the most populous countries in the world, and also some of the smallest and least populated island-states in the Pacific.The region boasts of economic powers such as Japan, and also some of the least developed.Climatically, there is a whole range from the harsh continental type to the mild breezy conditions in the Pacific Islands.In ethno-cultural terms, we have Mongoloids, Caucasians, Polynesians, Melanesians and others.All these have a bearing on cancer patterns.
Singapore is essentially Asia in microcosm.It is situated in the middle of South-east Asia, at one of the important crossroads between the West and the East, including the Pacific.It is a veritable human laboratory for the study of human disease, with some 3 million people on an island of about 650 sq.km.
The ethnic distribution comprises 77% Chinese, 14% Malays and 7% Indians.In the last 25 years, foreign-bom migrants have declined from about 25% in 1970 to 15% in 1990.
The Chinese in Singapore are mainly derived from the south-eastern provinces of Fujian and Guangdong in China.The Malay population is largely derived from the neighbouring countries of Malaysia and Indonesia, while the term "Indian" refers to all persons from the indigenous populations of India, Pakistan, Bangladesh and Sri Lanka (Ceylon).
The population-based Cancer Registry started operations on 1 January 1968.It has to-date published four reports, besides contributing to the IARC publication `Cancer Incidence in Five Continents'.The latest report documents the incidence trends over the last 25 years') Some of the results will be pre- sented in the context of the situation in the Asia-Pacific region, based on the latest (1985) estimates of worldwide incidence2).
The 1985 estimates indicated that the total number of new cancer cases (excluding non-melanoma skin cancer) was 7.6 m, of which 52% were in developing countries.The most common cancer worldwide was lung cancer -11.8% in both sexes.Second was stomach (9.9%) and third breast (9.4%).Among females only, breast comprised almost 20% of all sites (Table 1).

ALL SITES
In the 10-year period 1983-1992, there were an average of 4800 new cases per year in Singapore.On the whole, the majority of cases occur among the Chinese, with Malays having the lowest risks.In the Asia-Pacific region, the total number of cases ranged from 700 in Micronesia/Polynesia to 1.52 m in China alone.
The top 5 cancer sites for each of the three main ethnic groups are given in Table2.

SELECTED SITES (a)Lung
Lung is still the most common primary site in the world, having increased 36% over the 1980 estimates.In Singapore, the Malays have 50% and Indians 30% of the risk in Chinese.The Indians in Singapore and Bombay are among the populations with the lowest risks.While the rates in Chinese have reached a plateau, the Malay males have shown increases from 14.8 per 100,000 in 1968-72 to 37.2 in 1988-92.It is also worth noting that the proportion of adenocarcinomas among females has increased from 18.8% to 48.1% in 20 years.
In a recent 20-year follow-up study of 3361 smokers in Singapore, the relative risk of lung cancer death was 13.2 in males and 6.4 in females3).The high incidence of lung cancer, particularly adenocarcinoma, among female Chinese is still a research question, the suspicion being mainly directed at dietary factors.

(b)Stomach
Stomach cancer is the second most common site in the world.Although still an important site in Singapore, it is declining at about 2% per annum.The Chinese have very high rates, particularly the Hokkien and Teochew dialect groups.In the Asia-Pacific region, Japan remains the country with the highest rates, and Singapore Chinese comes between those in Shanghai and Hong Kong.

(c)Breast
Breast is the most frequent site worldwide among females, and it is also the case in Singapore.Generally, in Asia it is low (at around 20 per 100,000), but the rates are increasing.In Singapore, there is a clear increase over the last 25 years in all three ethnic groups, with the age-adjusted risk ratio for 1988-92 being twice that in 1968-72.
A recent study in Singapore attributed the increasing trend to a strong cohort effect and suggests that the incidence is likely to increase even further in the future4) It also provides support for the role of demographic and lifestyle factor changes as possible risk factors.A case-control study completed in 1989 showed increased risks associated with family history of breast cancer, nulliparity, and high intake of red meat.Protective effects were suggested for PUFA, beta-carotene and high soya to total protein intake5,6) Colorectal cancer is the second most common site in the developed world.In Asia, it is still relatively low (about half or less) although some populations have reported increases e.g.Japan, Hong Kong and Singapore.In Singapore, the incidence has been increasing in the last 20 years at the average rate of about 3% per annum.Our rates are fast approaching those for Chinese in Hawaii and Los Angeles.Among the ethnic groups, Malays and Indians have rates that are about half the Chinese, with local-borns having higher risks than the foreign-borns.This is very much in line with the experience in Australian and North America where immigrants have attained the rates of their host countries within one generation.
A case-control study in Singapore showed a predisposing effect of a high meat to vegetable consumption ratio and a protective effect of high cruciferous vegetable intake7).

(e)Cervix
Cervical cancer is very much a cancer of the developing world, especially in Africa, South Asia and South America.The lowest rates are in West Asia.In Singapore, the rates have been declining marginally.Among Indian females, it is still the second most common site.Malay females have much lower risks (60% of Chinese and Indians).

(I)Mouth and Pharynx
Cancers of the oral cavity and pharynx show large regional variations.Worldwide, high incidence is reported in South Asia and Melanesia (Papua New Guinea), all of which are attributable to the chewing of betel leaf, areca nut, lime, and tobacco in varying mixtures.
In Singapore, the incidence among Indians is markedly higher than the other ethnic groups, for both sexes.There is, however, evidence of a decrease especially among Indian females, probably due to the declining habit of chewing.
(g)Nasopharynx In East Asia, a special cancer is the nasopharyngeal carcinoma which mainly affects southern Chinese in China, Hong Kong, Singapore and USA.All these high incidence areas have rates around 20 per 100,000 or above and they have remained stable in the last 25 years.The intermediate group (about 5 per 100,000) includes Malays and some other indigenous groups (Thais, Vietnamese, Kadazans and Dyaks) in South and East Asia.Most other populations have low rates of less than 1, including Indians in Singapore.
A recently completed case-control study in Singapore showed significantly increased risks in association with consumption of salted soya beans, canned pickled vegetables, 'sze chuan chye' and `kiam chye' (salted vegetables)8).A protective effect of high vitamin-E intake was also obaerved.These findings are quite similar to those found in China, although the data were insufficient to confirm the effect of salted fish in its aetiology.Other studies in Singapore also confirmed the interactive roles of genetic susceptibility (as shown by the HLA profile) and the Epstein-Barr virus as well9).

(h)Liver
Primary liver cancer is largely a problem of developing countries, with high incidence in East Asia and Melanesia.It has been estimated that China accounts for 44% of the world's cases.In Singapore, incidence continues to show a steady decline for both sexes, with the Chinese having the highest rates.There is now general acceptance that the disease is mainly due to the interaction of Hepatitis B and C viruses and exposure to aflatoxin10).

CONCLUSION
The small and compact population of Singapore, with its efficient organization and easy access to effective health care has enabled good epidemiological studies to be conducted.In the last two decades, we have made useful contributions to the understanding of cancer patterns and also the development of aetiological hypotheses.We will continue to monitor the situa-

Table 1 .
Worldwide distribution of cancer cases by site and sex, 1985.

Table 2 .
Most frequent cancer sites in Singapore, by sex and ethnic group, 1988-1992.