title: Decline in incidence of endometrial cancer following increase in prescriptions for opposed conjugated estrogens in a prepaid health plan.
abstract: During the 1980s, the ecologic association of conjugated estrogens with endometrial cancer changed from positive to negative in a prepaid health plan. During the same period, use of progestins increased dramatically. We investigated whether the latter increase could explain the reversal of the estrogen-cancer association. Endometrial cancer incidence was estimated from cases recorded in the health plan registry divided by the number of women over age 45 years. Conjugated estrogens usage was measured as milligrams prescribed per woman per year and progestin was measured as tablets per woman per year, both based upon pharmacy records. Graphical and regression methods were used to analyze the resulting ecologic data. In a log-linear regression of incidence on conjugated estrogens and medroxyprogesterone usage, estrogen usage had a strong positive association with incidence, while medroxyprogesterone had a strong negative association with incidence. The change in the direction of the ecologic association between estrogen and endometrial cancer that occurred in 1984 continued until 1993, suggesting that the decline in endometrial cancer incidence and concomitant increase in conjugated estrogens usage since 1984 is explained by the increasing use of progestins. The data are entirely consistent with the hypothesis that progestins can protect against most of the excess risk conferred by conjugated estrogens, although the ecologic nature of the data prohibits drawing further inferences.
authors.affiliation: Department of Obstetrics and Gynecology, Kaiser Permanente Medical Center, Los Angeles, California 90027, USA.
authors.forename: H K
authors.initials: HK
authors.lastname: Ziel
authors.forename: W D
authors.initials: WD
authors.lastname: Finkle
authors.forename: S
authors.initials: S
authors.lastname: Greenland
mesh_terms: D000230:Adenocarcinoma / Q000453:epidemiology* / Q000517:prevention & control; D004358:Drug Therapy / Q000706:statistics & numerical data; D016889:Endometrial Neoplasms / Q000453:epidemiology* / Q000517:prevention & control; D004966:Estrogens, Conjugated (USP) / Q000627:therapeutic use*; D005260:Female; D006279:Health Maintenance Organizations; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D009017:Morbidity / Q000639:trends; D011372:Progestins / Q000627:therapeutic use*
chemical_list: D004966:Estrogens, Conjugated (USP); D011372:Progestins