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CUSHING KARA L. MS; WEISS, NOEL S. MD, DrPH; VOIGT, LYNDA F. PhD; MCKNIGHT, BARBARA PhD; BERESFORD, SHIRLEY A. A. PhD
Obstetrics & Gynecology: January 1998
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Objective To determine whether a low dosage (0.3 mg/day) of unopposed conjugated estrogens can be used without incurring an elevated risk of endometrial cancer.

Methods In this case-control study, cases (n = 484) consisted of women diagnosed with endometrial cancer between 1985 and 1991 in three counties in Western Washington. Controls (n = 780) were identified using random digit dialing within the same three counties. Subjects were interviewed in person to obtain basic demographic and medical history information, as well as specific information about hormone use.

Results Eighteen cases and eight controls had taken 0.3 mg/day of unopposed conjugated estrogens and no other dose or preparation of estrogens (risk relative to that of women who had not taken postmenopausal hormones = 5.4, 95% confidence interval [CI] 2.3, 13.0). The risk was particularly high in women whose use of this dose was both current and of more than 8 years' duration (odds ratio = 9.2, 95% CI 2.9, 29.0). The elevation in risk in users of 0.3 mg/day was similar in size to that associated with the daily unopposed use of 0.625 mg of conjugated estrogens.

Conclusion The results suggest that a dosage of 0.3 mg per day of unopposed conjugated estrogens is associated with an increased risk of endometrial cancer.

Address reprint requests to: Kara L. Cushing, MS, Fred Hutchinson Cancer Research Center, PO Box 19024, 1100 Fairview Avenue North, MP381, Seattle, WA 98109-1024. E-mail: kcushing@fhcrc.org

© 1998 The American College of Obstetricians and Gynecologists

The risk of endometrial cancer is increased among women who use 0.3 mg per day of unopposed conjugated estrogens.