A case-control study of breast cancer among Japanese women in Tokyo

Abstract

To explore the risk factors for recent female breast cancer, a hospital-based case-control study was conducted in Tokyo, from 1990 to 1991. Information on potential risk factors was obtained by a self-administered questionnaire from 5.084 out-patients. Of the patients, 300 incident breast cancer cases were recruited, and 900 age-matched controls were randomly selected. Significant findings are: (a) the more the number of livebirths, the smaller the risk in premenopausal women (adjusted relative risk (RR)for 3 or more births relative to none: 0.24; 95% confidence interval (Cl): 0.08-0.65); (b) in premenopausal women, regular menstrual cycle increased the risk (adjusted RR: 2.50, 95% Cl: 1.16-5.38), and its increasing duration decreased the risk (P for linear trend <0.05); (c) current smokers experienced an increased risk (1.63, 1.11-2.39 for all women and (2.73; 1.38-5.39) for postmenopausal women; (d) obese women were at a greater risk of postmenopausal breast cancer: adjusted RR for those weighing 70 kg or more relative to those weighing 50 kg or less being 4.82 (95% Cl: 1.53-15.2); (e) the later the age at first livebirth, the higher the postmenopausal breast cancer risk (2.85; 1.16-6.99 and 3.54; 1.03-12.2 for ages of 30-34 and 35 years and more, respectively). Neither premenopausal nor postmenopausal breast cancer risk was independently associated with family history of breast cancer, history of benign breast disease, ages at menarche and menopause, lactation, drinking habits and body height.