Breast cancer is the most common cancer among women worldwide, accounting for 1 in 4 cancer diagnoses in women. The use of hormonal contraceptives, particularly those containing estrogens and progestagens, has recently increased the risk of breast cancer. However, the risk appears to decline after cessation, and no excess risk has been observed ten or more years after stopping use.
According to a study published in PLOS Medicine, a meta-analysis of worldwide evidence on breast cancer risk associated with combined oral contraceptives was conducted. The study found a slightly increased risk of breast cancer in current or recent users, with no apparent excess risk observed ten or more years after stopping use. However, at that time, limited information was available on the risks associated with hormonal contraceptives containing only progestagens.
Since then, there has been limited published evidence on premenopausal breast cancer risk associated with using progestagen-only contraceptives. Different types of hormonal contraceptives have also changed over time, with recent increases in the use of progestagen-only preparations such as oral and long-acting parenteral formulations (injectables, implants, and progestogen-releasing intrauterine devices). In England, for example, the prescription rate for oral progestagen-only contraceptives roughly doubled over the last decade. They will account for nearly as many prescriptions as oral combination contraceptives by 2020.
With the growing popularity of progestagen-only contraception, reliable evaluation of their influence on breast cancer risk is critical. The findings of this study suggest that more excellent research into the relationship between progestagen-only contraception and breast cancer risk is needed to inform better clinical practice and the decisions women make when selecting a method of birth control.
Hormonal contraceptives include combined oral contraceptives containing estrogen and progestagen, oral progestagen-only contraceptives, injectable progestagens, and progestagen-releasing intrauterine devices (IUD). The study showed that the odds ratios (ORs) for each hormonal contraceptive were statistically significant but relatively small, ranging from around 1.2 to 1.3, with no significant difference between the different hormonal contraceptive types. The average time between the last prescription and breast cancer diagnosis was about three years, meaning these results generally apply to current or recent users of these hormonal preparations.
The doses of estrogen and progestagen constituents in combined oral contraceptives have decreased over the years, and the preparations used by women in the study were likely to have been of lower doses, on average, than those used by women in previously published meta-analyses. However, the findings from both studies are consistent.
The most startling finding of the current study is that progestagen-releasing contraceptive IUDs are linked with an elevated risk of breast cancer, equivalent to the higher risks observed for oral and other parenteral progestagens. Previous prescriptions for various hormonal contraceptives were unlikely reasons for this overstock.
The study anticipated that breast cancers might be overdiagnosed in women who visit their family physicians often (GPs). No such differences were seen, and the lack of an elevated risk of breast cancer about other commonly given drugs provides more evidence against the potential of a detection bias.