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 involving 1086 women (204 cases and 882 controls) was conducted to determine significant factors associated with the risk of breast carcinoma among Chinese women in Singapore ages 45 to 69 years. METHODS. A forward stepwise logistic regression model adjusted for confounding variables of age, age at menarche, menopausal status, parity, age at first and last delivery, use of oral contraceptives, hormone replacement therapy, family history of breast carcinoma, history of benign breast biopsy, 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 trend). Significant trends were also noted for increasing height and breast carcinoma risk (P = 0.003, chi-square test). Women who were taller than 159 cm (OR: 2.3; 95% CI, 1.4-3.9) had approximately twice the risk of women shorter than 150 cm. Body mass index as a measure of generalized obesity did not significantly predict risk for breast carcinoma. Reproductive and menstrual factors significantly related to risk for 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 replacement therapy (OR: 0.54; 95% CI, 0.3-0.9; P = 0.01). Previous breast biopsy for benign disease was also associated with a higher risk for 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 associated with changes in lifestyle related to caloric intake (central obesity and height) and reproductive or menstrual factors (number of deliveries, age at last delivery, age at menopause, and breast feeding). Better and excess nutrition in early and later years of life and fewer births (related to rapid urbanization) may explain in part the increasing incidence of breast carcinoma occurring in Singapore. (C) 1997 American Cancer Society.