Contemporary Hormonal Contraception and the Risk of Breast Cancer.
Morch et al. use data from nationwide registries in Denmark to examine contemporary hormonal contraception and the risk of breast cancer. A potential confounder was the age of the women at first birth since the risk of breast cancer is lower among women who give birth for the first time at an early age than among older women who do and a woman's age at first birth is delayed by contraception. Data on age at first birth were abstracted from the Danish National Birth Register which started in 1973. These data may be missing for older cohort members. Data should be complete for women younger than 35 years of age so Table S7 in the Supplementary Appendix of the article is important. However the authors' analysis was not adjusted for the women's age at first birth. An important omission was a discussion of how many women underwent tubal sterilization and whether they were placed disproportionately into the "never used hormonal contraception" category. Information about sterilization is available from the Danish National Health Register; this information is complete from 1977 on. This information again may be incomplete for older cohort members. Evidence that sterilization may lower the risk of breast cancer makes this an important issue. Women may choose to delay childbearing even knowing that it will increase their risk of breast cancer. They should not conclude from this study that this risk can be avoided by choosing "nonhormonal" contraceptive methods of an unspecified type and efficacy. (full text)
The New England journal of medicine