The Epidemiology of Breast Cancer in Singapore

Breast cancer is the most frequent cancer in Singapore, which showed rapid increase in incidence in the last two decades. A case-control study consisted of 200 histologically confirmed cases and 420 controls was carried out between 1986 and 1988. The results were as follows; in premenopausal women, the increased risk was associated with high red meat intake and high animal protein intake and the decreased risk was associated with high polyunsaturated fatty acid (PUFA) intake, high soya protein and total soya intake, high PUFA: SFA (saturated fatty acids) ratio, and high soya/total protein. The significant factors after multiple regression analyses of dietary effects were predisposing effect of red meat and protective effect of high intake of PUFA, b-carotene and soya/total protein. In postmenopausal women no significant factors were found for any of dietary effects. The findings were mainly confined to younger premenopausal women who have exhibited major changes in their diet.


INTRODUCTION
Although breast cancer is the most frequent cancer in Singapore, the incidence rates are about half those of the Western Caucasian populations.Within Asia, the rates in Singapore and Hong Kong are very similar to those of US Chinese, the these are about twice those in China (Shanghai) and Japan(1) Indian populations have rates in between, and Malays the lowest rates known.Thus, it can be seen that breast cancer remains very much a problem of the developed Western world.

Descriptive Studies
The most striking epidemiological feature of this cancer in Singapore is the rapid increase in incidence in the last two decades.The latest age-standardized incidence rates ASIR, (1983)(1984)(1985)(1986)(1987) for the main ethnic group in Singapore are as follows: It would be useful and interesting to try and determine the possible reasons for the increase in the younger women, most of whom are premenopausal.Because of our highly successful population control programme, fertility in Singapore women has declined markedly since 1965 with the implementation of the First National Family Planning Programme .Looking at age-specific fertility rates, the decline is very strong in the age-groups 20 to 34 years(3).
At the same time, Singapore has undergone dramatic changes on the socio-economic scene.With rising affluence in an open economy, lifestyles have become more Westernized and this includes dietary patterns as well.In the 20-year period , food availability has increased dramatically.Increases were seen for meat (135%), fat, especially from animals (73%), eggs (79%) and fruits (61%).In terms of nutrient availability, per capita calorie supply has increased 25%, protein 34% and fat 67%("1.

An Analytical Study
Between 1986 and 1988, we conducted a case-control study among Singapore Chinese women (5).The numbers in the other two major ethnic groups are too small for meaningful study.After eliminating some refusals and unsatisfactory cases (including diabetics) , we managed to accrue 200 histologically confirmed incident cases.Controls were selected from general surgery, eye and orthopaedic wards of the same hospitals and group-matched within 5-year age groups.In all, we had 420 controls.
All subjects were interviewed by trained investigators, using a quantitative food frequency questionnaire to determine usual dietary intake one year before interview.Based on past literature, information on sources of the following nutrients were obtained: -animal and non-animal protein -fat -saturated fatty acids (SFA) -monounsaturated fatty acids (MUFA) -polyunsaturated fatty acids (PUFA) -cholesterol , caffeine and methylxanthines In terms of food groups, the following were of particular interest: -total red meats -coffee -total fish -total soya products Alcohol intake was not assessed as Chinese women were thought to take little of the drink.For the analysis, intakes of nutrients and foods were categorized into tertiles of the control range and fitted into the multiple logistic regression model.Data for the premenopausal and postmenopausal (at least 1 year after cessation of menses) were considered separately, and adjustments for relevant non-dietary variables were made in each group.
The results point to important differences in the epidemiology of premenopausal breast cancer and the postmenopausal group.Premenopausal women comprised 54% of cases and 49% of controls.While one cannot rule out endocrinal explanations, the more likely reason is because of the many dietary and other changes occurring in the younger group.Heterogeneity in dietary intakes in the postmenopausal group was insufficient to show differences and comparisons generally lacked statistical power.

Premenopausal Group
The main findings in premenopausal women were as follows: