LAUSR

A prospective study of 1.8 million Danish women made headlines in late 2017 when it suggested that hormonebased contraception might raise the risk of breast cancer slightly.1 Even modern versions that release lower levels of estrogen and progestin compared with their predecessors were associated with a higher risk. It appeared that no modern hormone-based method was entirely risk free. However, other studies and experts have suggested that the relative and absolute risks may be far more nuanced, especially when balanced with the benefits. Communicating the potential tradeoffs can be critical for patients, who often lack a good understanding of what it really means for them. Nevertheless, the divergent reactions to the Danish study demonstrate how cancer researchers and other specialists can view the same pros and cons through very different lenses. Breast cancer is relatively rare among the group of women most likely to be using birth control: those in their 20s and 30s. For example, a 20-year-old has a 1-in-1732 chance of developing breast cancer within the next decade. That risk increases with age: for a 40-year-old, the odds of developing breast cancer within the next 10 years are approximately 1 in 50. The study, which followed participants for an average of nearly 11 years, estimated that using hormonal contraception increased a woman’s relative risk by approximately 20% compared with their counterparts who did not use it. In absolute terms, that increase translates into an additional 13 breast cancer cases per year for every 100,000 women using hormone-based contraception, or 1 extra case for every 7690 women. Lead author Lina Mørch, PhD, MSc, a research epidemiologist at the University of Copenhagen in Denmark, says other pros and cons should be considered, but that physicians should be obligated to inform women about the small but persistent breast cancer risk. Anne McTiernan, MD, PhD, a cancer prevention researcher at the Fred Hutchinson Cancer Research Center in Seattle, Washington, agrees that the higher risk, albeit modest, was statistically significant and increased with a longer duration of contraception use. Although the study did not examine subgroups according to genetic mutations or modifiable risk factors such as alcohol use, she says, “women who are at increased risk for any reason may want to limit use of hormonal contraceptives.”