Menopause and Breast Cancer Risk2

Age at menopause and type of menopause from hospital records of breast cancer patients were compared with similar information reported by a national probability sample of women. The cancer series consisted of 3,887 patients selected from those reported to the Connecticut Cancer Registry between 1950 and 1959. The national sample comprised 3,581 women responding to the National Health Examination Survey of 1960–1962. The validity of the comparison and the effect of the relatively large number of breast cancer patients whose menopause histories were deficient were evaluated; no substantial bias was identified. Overall, surgically induced menopause was associated with a reduction in breast cancer risk to about 60% of that experienced by women having natural menopause at ages 45–54. The decrease was greatest for those with menopause induced before age 35, but induction up to age 50 was protective. Little effect occurred in the decade following the surgical procedure, but substantial reduction occurred in all subsequent periods. Among women with menopause induced before age 35, breast cancer risk remained as low as one-third that expected 30 and more years later. Relative risk of breast cancer increased with age at natural menopause. Women with natural menopause at age 55 or older had twice the breast cancer risk experienced by those whose menopause occurred before age 45. The relative risk of breast cancer associated with late natural menopause was greatest after age 70. These findings illustrate the long period which may elapse between etiologic events and the appearance of human cancer, and they imply that the ovarian etiology of human breast cancer is not restricted to cancers appearing during the years of active ovarian function.