Women who use oral contraceptives have reduced risks of ovarian and endometrial cancer. This protective effect increases with the length of time oral contraceptives are used.
Oral contraceptive use is associated with an increased risk of cervical cancer; however, this increased risk may be because sexually active women have a higher risk of becoming infected with human papillomavirus, which causes virtually all cervical cancers.
Women who take oral contraceptives have an increased risk of benign liver tumors, but the relationship between oral contraceptive use and malignant liver tumors is less clear.
What types of oral contraceptives are available in the United States today?
Two types of oral contraceptives (birth control pills) are currently available in the United States. The most commonly prescribed type of oral contraceptive contains man-made versions of the natural female hormones estrogen and progesterone. This type of birth control pill is often called a “combined oral contraceptive.” The second type is called the minipill. It contains only progestin, which is the man-made version of progesterone that is used in oral contraceptives.
How could oral contraceptives influence cancer risk?
Naturally occurring estrogen and progesterone have been found to influence the development and growth of some cancers. Because birth control pills contain female hormones, researchers have been interested in determining whether there is any link between these widely used contraceptives and cancer risk.
The results of population studies to examine associations between oral contraceptive use and cancer risk have not always been consistent. Overall, however, the risks of endometrial and ovarian cancer appear to be reduced with the use of oral contraceptives, whereas the risks of breast, cervical, and liver cancer appear to be increased (1). A summary of research results for each type of cancer is given below.
How do oral contraceptives affect breast cancer risk?
A woman’s risk of developing breast cancer depends on several factors, some of which are related to her natural hormones. Hormonal and reproductive history factors that increase the risk of breast cancer include factors that may allow breast tissue to be exposed to high levels of hormones for longer periods of time, such as the following:
Beginning menstruation at an early age
Experiencing menopause at a late age
Later age at first pregnancy
Not having children at all
A 1996 analysis of epidemiologic data from more than 50 studies worldwide by the Collaborative Group on Hormonal Factors in Breast Cancer found that women