RISK OF ENDOMETRIAL CANCER IN RELATION TO USE OF LOW-DOSE, UNOPPOSED ESTROGENS

Objective: To determine whether a low dosage (0.3 mg/day) of unopposed conjugated estrogens can be used without incurring an elevated risk o f endometrial cancer. Methods: In this case-control study, cases (Ir = 484) consisted of women diagnosed with endometrial cancer between 198 5 and 1991 in three counties in Western Washington. Controls (n = 780) were identified using random digit dialing within the same three coun ties. 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 prepara tion of estrogens (risk relative to that of women who had not taken po stmenopausal hormones = 5.4, 95% confidence interval [CI] 2.3, 13.0). The risk was particularly high in women whose use of this dose was bot h 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 o f 0.3 mg per day of unopposed conjugated estrogens is associated with an increased risk of endometrial cancer. (C) 1998 by The American Coll ege of Obstetricians and Gynecologists.