A recent preliminary research analysis found a link between breast cancer and those who take oral contraceptives.
Birth control pills containing high doses of estrogen, along with some other formulations, may increase the risk of breast cancer in women under 50, the research suggests.
“There are numerous oral contraceptive formulations,” explained lead researcher Elisabeth Beaber, a staff scientist at the Fred Hutchinson Cancer Research Center in Seattle. “Some of these formulations increase breast cancer risk while other formulations do not raise risk.”
In the study, researchers examined health records and oral contraceptive use in 1,102 women ages 20 to 49 years diagnosed with breast cancer and 21,952 women without breast cancer in the same age group. Unlike some other studies on the safety of contraceptive use that relied on data depending on women’s self-report or recall, this study was based on electronic pharmacy records that included the drug name, dosage and duration of medication use.
Women who had used high-estrogen pills or those with high synthetic progestin in the past year were about 2.6 times as likely as women who had not used oral contraceptives to be diagnosed with breast cancer. Women who used norethindrone (Aygestin), a progestin-only pill, in triphasic dosing were 3.1 times more likely to have a breast cancer diagnosis.
The study found no relationship between an increased cancer risk and the use of low-dose estrogen pills, which are currently the most commonly prescribed type of birth control pills in the U.S., according to experts not involved in the study.
Some past research suggests that the hormones in birth control pills could “feed” hormone-sensitive tumors and thereby raise younger women’s risk of a breast cancer diagnosis, or of developing more aggressive cancers.
Birth control pills have evolved over the decades since their introduction and the hormone doses they contain have dropped steadily, so many studies are based on data for formulations that are no longer used, Beaber and her colleagues point out in the journal Cancer Research.
“Our results suggest that use of contemporary oral contraceptives [birth control pills] in the past year is associated with an increased breast cancer risk relative to never or former oral contraceptive use, and that this risk may vary by oral contraceptive formulation,” study author Elisabeth F. Beaber, a staff scientist in the Public Health Sciences Division of Fred Hutchinson Cancer Research Center in Seattle, Washington, said in a statement.
Beaber and her co-authors acknowledge that their results “should be interpreted cautiously” and further studies with a larger group of women are needed to confirm the findings.
“It is important to remember that breast cancer is rare among young women and that there are other established health benefits associated with oral contraceptive use,” Beaber said.
The new findings were published today in the journal Cancer Research.