Early adult body weight, body mass index, and premenopausal bilateral breast cancer: data from a case-control study.

Previous studies using current or recent adult body weight and body mass index are inconclusive as to a possible effect of increased body mass on premenopausal breast cancer incidence. Only five studies have presented data on early adult body mass, and no study has reported these data for premenopausal bilateral breast cancer. Because premenopausal bilateral breast cancer is assumed to be partly genetic and partly environmental in origin, it is crucial to identify possible modifiable risk factors for this cancer. We present data on early adult body weight and body mass (Quetelet Index, QI) from a case-control study of 142 premenopausal bilateral breast cancer cases from Los Angeles County, California, Connecticut, and Quebec, Canada, and 229 sister controls. The odds ratio (and 95% confidence interval) of premenopausal breast cancer adjusted for age, education, alcohol consumption, and oral contraceptive use was 0.7 (0.3-1.4) for women in the highest tertile of QI at age 18. The results do not suggest that elevated body mass index at a young age increases the risk of premenopausal bilateral breast cancer, but lend only weak support to the hypothesis of an inverse association between body mass index and premenopausal breast cancer.