Oral contraceptives were introduced in the 1960s and helped launch the sexual revolution. Since that time, studies have come up with varying and sometimes conflicting findings on the cancer risk oral contraceptives may pose. Some studies have suggested women using them could have a reduced risk of endometrial and ovarian cancer.
The findings about the use of oral contraceptives and breast cancer risk have been inconsistent — with some showing an increased risk of breast cancer among women using oral contraceptives, some showing no increased risk, and others suggesting a protective effect long-term.
To get a clearer picture of the risks — and potential benefits — of oral contraceptives, Swedish researchers undertook an observational study of both the long-term and time-dependent association between oral contraceptive use and cancer risk.
Even 15 years after discontinuing oral contraceptives, the risk of endometrial and ovarian cancer was reduced by 50 percent.
The study findings should provide useful information for determining lifetime cancer risk associated with taking oral contraceptives. “The results will allow women and their doctors to make more informed decisions about oral contraceptive use, so they represent an important step towards personalized medicine,” the researchers said.
More than 255,000 women who were born between 1939 and 1970 were included in the UK Biobank data used in the study. Self-reported data and data from national registries were collected to gather information about cancer diagnoses.
“It was clear that women who had taken oral contraceptives had a much lower risk of developing endometrial and ovarian cancer,” Asa Johansson, corresponding author on the study, said in a statement. Even 15 years after discontinuing oral contraceptives, the risk was reduced by 50 percent.
Oral contraceptive use was associated with an increased risk of breast cancer, but this increase was only seen for at most two years after discontinuation.
When the researchers looked at data from when women entered the study until they turned 55 years old, oral contraceptive use was associated with an increased risk of breast cancer. However, this increase was only seen for at most two years after discontinuation.
Johansson, an assistant professor of immunology, genetics and pathology at Uppsala University, said her team was surprised they only found a small increase in breast cancer risk among oral contraceptive users, a risk that disappeared a few years after discontinuation. “Our results suggest the lifetime risk of breast cancer may not differ between ever and never users, even if there is an increased short-term risk.”
The study is published in Cancer Research.