Some Birth Control Pills May Up Breast Cancer Risk
High-dose estrogen formulations linked to greater risk in women under 50, experts find
By Kathleen Doheny
THURSDAY, July 31, 2014 (HealthDay News) -- Birth control pills containing high doses of estrogen, along with some other formulations, may increase the risk of breast cancer in women under 50, new preliminary 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."
Overall, birth control pill use within the past year was associated with a 50 percent increased risk of breast cancer risk compared with former use or no use of birth control pills, Beaber found.
This study was designed to find a possible link between oral contraceptive use and breast cancer risk in younger women. But, it wasn't designed to prove that birth control pills definitively cause the increased risk. However, the researchers did take into account other factors that increase breast cancer risk, such as family history. In addition, they found that the link was slightly stronger -- though not statistically significant -- for breast cancers termed estrogen-receptor positive. This type of cancer needs estrogen to grow, which might help explain why high-dose estrogen pills elevated risk.
The researchers also found variations in risk among different formulas, with low-dose estrogen pills appearing safest. "Recent use of oral contraceptives containing low-dose estrogen [20 micrograms ethinyl estradiol] did not appear to increase breast cancer risk," Beaber said.
These lower-dose pills account for an increasing number of prescriptions written today, Beaber said.
Which formulations seemed to raise the risk of breast cancer? High-dose estrogen pills -- those containing 50 micrograms ethinyl estradiol or 80 micrograms mestranol -- were associated with nearly a three-fold higher risk of breast cancer, she said. Triphasic combination pills with 0.75 milligrams of norethindrone were linked to more than a three-fold higher risk of breast cancer, according to Beaber.
Pills with ethynodiol diacetate -- a progestin -- appeared to increase the risk of breast 2.6 fold, Beaber said.
Risks seemed lower with moderate-dose estrogen pills -- those with 30 to 35 micrograms of ethinyl estradiol or 50 micrograms mestranol were linked to a 1.6 times higher risk of breast cancer.