Breast Cancer in Premenopausal and Postmenopausal Women2

Abstract

A case-control study was done to determine if the risk factors for breast cancer differed between premenopausal and postmenopausal women. Cases were 95 premenopausal and 278 postmenopausal women with breast cancer admitted to the Ontario Cancer Foundation Clinic, London, Canada, during a 45-month period. Controls were 106 premenopausal and 480 postmenopausal women with benign and malignant disease of sites other than breast, admitted to the same clinic during the same period. Breast cancer risk increased with increasing age at first pregnancy among postmenopausal women only. Among premenopausal women, increased breast cancer was associated with early menarche. Late age at natural menopause was an important risk factor for postmenopausal women; the risk in women experiencing natural menopause over the age of 55 was 2.5 times as great as that of women undergoing menopause before age 40. A longer interval between age at menarche and age at first pregnancy increased the risk in both groups. Use of oral contraceptives, or duration of use, did not increase the risk of breast cancer. Among oral contraceptive users, there was a trend toward greater risk with increasing age at first use of oral contraceptives.