Abstract
5,160 non-hysterectomised women aged 44-100 years completed a health survey questionnaire as part of a longitudinal study of a southern California retirement community begun in June 1981. As of 1 January 1987, 50 incident cancers of the endometrium had occurred among these women, who had contributed 23,786 years of follow-up. Women who had used oestrogen replacement therapy had a relative risk of endometrial cancer of 10 compared to women who had never used oestrogens (P less than 0.0001). Risk increased with increasing duration of use (chi 2 test for trend = 50.60, P less than 0.0001); women who had used oestrogens for 15 or more years had a relative risk of 20 (95% C.I. = 7.2, 54) compared to non-users. While current and recent users (i.e. those who had used oestrogen within one year of the initial survey) had the greatest risk (RR = 25, 95% C.I. = 9.2, 69), women who had last used oestrogens 15 or more years ago still had a significantly increased risk (RR = 5.8, 95% C.I. = 2.0, 17). No other variable studied had a major effect on risk, except smoking. Women who smoked at the time of menopause had a significantly reduced risk of disease (RR = 0.38, P = 0.005), which was essentially unchanged after adjustment for oestrogen use.
Highlights
Previous studies of oestrogen use in this community have found extremely good correlation in relative risks for various chronic diseases when oestrogen use was ascertained by interviews, medical records or pharmacy records (Mack et al, 1976; Ross et al, 1980; Paganini-Hill et al, 1981)
This study confirms in a population-based cohort that the risk of endometrial cancer increases sharply with increasing duration of usage of oestrogen replacement therapy
Other reports have shown that the elevated risk persists after cessation of oestrogen use (Mack et al, 1976; Weiss et al, 1979; Shapiro et al, 1985), but this study extends the risk to longer drug-free intervals
Summary
It is well established that post-menopausal women who use oestrogen replacement therapy are at increased risk of endometrial cancer (Smith et al, 1975; Ziel & Finkle, 1975; Mack et al, 1976; McDonald et al, 1977; Gray et al, 1977; Autunes et al, 1979; Weiss et al, 1979; Jick et al, 1979; Jelovesk et al, 1980; Shapiro et al, 1980; Hulka et al, 1980). Most studies which have explored this association have been of the case-control design. The appropriate control series for such studies has been the topic of considerable scientific concern (Horwitz & Feinstein, 1978). Few prospective studies have evaluated the strength of this association (Hoover et al, 1976; Persson et al, 1986) and few of the case-control studies have contributed information on risk after lengthy periods off therapy. This paper reports the results of a large cohort study in which the prevalence of past oestrogen use was high
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