Women who recently used birth control pills had an increased risk of breast cancer, according to new research published in Cancer Research.
The study found that those women who used pills containing high-dose estrogen and a few other formulations had an increased risk, whereas women using some other formulations did not.
"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," said Elisabeth F. Beaber, PhD, MPH, a staff scientist in the Public Health Sciences Division of Fred Hutchinson Cancer Research Center in Seattle, Washington.
"Our results require confirmation and should be interpreted cautiously," added Beaber. "Breast cancer is rare among young women and there are numerous established health benefits associated with oral contraceptive use that must be considered. In addition, prior studies suggest that the increased risk associated with recent oral contraceptive use declines after stopping oral contraceptives."
The study of 1,102 women diagnosed with breast cancer they found that recent oral contraceptive use increased breast cancer risk by 50%, compared with never or former use.
All study participants were at Group Health Cooperative in the Seattle-Puget Sound area. Patients received a cancer diagnosis between 1990 and 2009.
Birth control pills containing high-dose estrogen increased breast cancer risk 2.7-fold, and those containing moderate-dose estrogen increased the risk 1.6-fold. Pills containing ethynodiol diacetate increased the risk 2.6-fold, and triphasic combination pills containing an average of 0.75 milligrams of norethindrone increased the risk 3.1-fold.
Birth control pills containing low-dose estrogen did not increase breast cancer risk.
Dr Caroline Dalton, Senior Policy Officer at Breakthrough Breast Cancer, said: “Previous research in this area has found similar results for higher dose birth control pills in terms of increased breast cancer risk but data from this study is welcome in that it tells us more about the differences between high and low dose options.
“Levels of oestrogen in the combined pill have decreased over the past 30 years. Whilst the researchers state that these findings require further investigation, we are a little closer to finding out whether or not newer, lower dose pills are associated with the same risk as the higher dose formulations more commonly used in the past.
“However, it is important to note that breast cancer is rare in women under the age of 40, regardless of whether or not they use the contraceptive pill. In addition, ten years after coming off the pill any increased risk will have disappeared leaving the chance of developing breast cancer at around the same level as those who’ve never taken the pill. We’d advise women with any concerns about starting or stopping the pill to talk through the options with their doctor.”