RISK-FACTORS FOR BREAST-CARCINOMA IN SINGAPOREAN CHINESE WOMEN - THE ROLE OF CENTRAL OBESITY

BACKGROUND. The incidence of breast carcinoma in Singapore has nearly doubled over the past 25 years. This prospective case-control study in volving 1086 women (204 cases and 882 controls) was conducted to deter mine significant factors associated with the risk of breast carcinoma among Chinese women in Singapore ages 45 to 69 years. METHODS. A forwa rd stepwise logistic regression model adjusted for confounding variabl es of age, age at menarche, menopausal status, parity, age at first an d last delivery, use of oral contraceptives, hormone replacement thera py, family history of breast carcinoma, history of benign breast biops y, smoking history, height, weight, body mass index, and waist to hip ratio was used. RESULTS, Central obesity as indicated by women with a larger waist to hip ratio was associated with highest risk for breast carcinoma (odds ratio [OR]: 9.18; 95% confidence interval [CI],4.8-17. 5 comparing last and first quintile; P < 0.0001, chi-square test for t rend). Significant trends were also noted for increasing height and br east carcinoma risk (P = 0.003, chi-square test). Women who were talle r than 159 cm (OR: 2.3; 95% CI, 1.4-3.9) had approximately twice the r isk of women shorter than 150 cm. Body mass index as a measure of gene ralized obesity did not significantly predict risk for breast carcinom a. Reproductive and menstrual factors significantly related to risk fo r breast carcinoma were number of deliveries [OR: 0.8 1; 95% CI, 0.7-0 .9; P < 0.001], age at last delivery (P = 0.03), and use of hormone re placement therapy (OR: 0.54; 95% CI, 0.3-0.9; P = 0.01). Previous brea st biopsy for benign disease was also associated with a higher risk fo r breast carcinoma (OR: 3.5; 95% CI, 2.1-5.7; P < 0.001). CONCLUSIONS. The authors conclude that the risk of breast carcinoma is strongly as sociated with changes in lifestyle related to caloric intake (central obesity and height) and reproductive or menstrual factors (number of d eliveries, age at last delivery, age at menopause, and breast feeding) . Better and excess nutrition in early and later years of life and few er births (related to rapid urbanization) may explain in part the incr easing incidence of breast carcinoma occurring in Singapore. (C) 1997 American Cancer Society.