- In a case-controlled study of 23,000 women, researchers found a 50% increased risk of breast cancer in women who had recently used certain types of birth control, compared with former users or women who never took birth control pills.
- The highest risk was associated with triphasic combination pills containing 0.75 mg of norethindrone.
- A lead researcher in the study cautioned that the findings should be interpreted carefully.
In this nested case-control study, 1,102 women who had been diagnosed with breast cancer were compared with 21,952 controls. Most of the women were in their forties. Birth control pills containing high-dose estrogen increased the risk of breast cancer 2.7-fold, while those containing moderate-dose estrogen increased the risk 1.6-fold.
By contrast, birth control pills containing low-dose estrogen had no impact on breast cancer risk. Birth control pills that contained ethynodiol diacetate were associated with a 2.6-fold increased risk. Finally, triphasic combination pills containing 0.75 mg of norethindrone (marketed as Ortho 75) were associated with a 3.1-fold increased risk of breast cancer.
According to one of the lead researchers, Dr. Elisabeth F. Beaber, a staff scientist at the Public Health Sciences Division of Fred Hutchinson Cancer Research Center in Seattle, Washington, “Our results require confirmation and should be interpreted cautiously. 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."