To the Editor.
—Steinberg et al1 use the technique of meta-analysis of 16 prospective trials to show a 1.3 relative risk (RR) of developing breast cancer in women who used estrogens for 15 years. This risk estimate was "largely due to" the three European studies that included both premenopausal women and users of synthetic estrogens, in whom the RR was 2.5. The RR of developing breast cancer in the 13 US studies, 11 of which included only postmenopausal women using conjugated estrogens, was not provided. It must be similar to a prior meta-analysis, limited to studies of only conjugated estrogen use in postmenopausal women,2 which demonstrated no increased risk of breast cancer. It is surprising that this important information was not provided, since this is the most relevant statistic for the American practitioner wishing to advise postmenopausal women on the relative risks and benefits of conjugated estrogen use.