Use of Oral Contraceptives and Risk of Cancer of the Uterine Corpus or Ovary. Two Case-Control Studies

Abstract

Objective: There has been convincing evidence from cohort and case-control studies that OC use reduces the risk of cancer of the uterine corpus and ovary. The effect of OCs with low estrogen content is less clear. We addressed this question within a case-control study. Patients and Methods: The cases were drawn from three German population-based cancer registers and several clinical cancer registries from 1999 to 2001. The age- and region-matched controls were drawn from the German Cohort Study on Women's Health. The data include information on the exposure and time, type and duration of exposure as well as time of occurrence of any outcome. Unconditional logistic regression was used to determine the association between OC use and the risk of cancer of the uterine corpus and ovary. Results: We analyzed 485 cases of cancer of the uterine corpus and 1570 age-matched controls and 419 cases of ovarian cancer and 1518 age-matched controls. The adjusted odds ratio [OR] for cancer of the uterine corpus and OC use was 0.36 (95% confidence interval [95% CI]: 0.28 to 0.45), and the OR for ovarian cancer was 0.48 (95% CI: 0.37 to 0.61). The risk both of ovarian cancer and cancer of the uterine corpus was reduced with increasing duration of OC use. This effect declined with increasing time since last use, but even persisted more than 10 years after stopping pill use. The comparison of users of low estrogen dose OCs versus never-users also showed a clear risk reduction for both cancer types. Conclusion: Use of OCs is associated with a markedly decreased risk of cancer of the uterine corpus and ovarian cancer, particularly with long-term use. This effect persists for years after stopping pill use. There is also a clear protective effect associated with lower estrogen dose OCs.