Research summary
December 2006
Research into oral contraceptive pill use and risk of pre-menopausal breast cancer
Summary
A review published in Mayo Clinic Proceedings examined 34 studies published in or after 1980 looking into a link between the use of the oral contraceptive pill and an increased risk of breast cancer. The review found oral contraceptive use slightly increased the risk of pre-menopausal breast cancer by 19 per cent overall compared with women who had never used the pill.
The study also examined oral contraceptive pill use in women who had not had children compared with those who had. The increased risk was found to be highest (52 per cent) in women who had used the pill for four years or more before the birth of their first child. The risk was lower (24 per cent) in women who had never had children. The lowest risk (15 per cent) was in women who used the pill after having their first child.
National Breast Cancer Centre comment
It is important to keep this research in context for several reasons.
Firstly, the authors of the review have acknowledged certain problems with their methods. These include a lack of information on the study participants’ family history of breast cancer and the difficulty in drawing a definitive conclusion from an analysis of many differing studies. Research examined in the review also dates back to 1980, so the oral contraceptive pill will be older, higher dose preparations.
Secondly, it is important to note that the effect of the oral contraceptive pill on a woman’s lifetime risk of developing breast cancer is small because the underlying risk of breast cancer is low at ages when women commonly use the pill. Other studies have shown that this increase in risk gradually decreases to normal levels ten years after stopping use of the pill.
The Mayo Clinic review is one of many studies which show hormones have a role to play in the development of breast cancer. The study is consistent with others showing use of the oral contraceptive pill and events such as having children later in life contribute to an increased risk of breast cancer.
The World Health Organization (WHO) has also acknowledged that the oral contraceptive pill slightly increases the risk of breast cancer, but has also said it decreases the risk of ovarian and endometrial cancers. Overall the WHO has stated that for most healthy women, the health benefits of the oral contraceptive pill clearly exceed the health risks.
For women at increased risk of breast cancer, the balance of benefits versus risks of being on the oral contraceptive pill may differ. Any woman concerned about the oral contraceptive pill or considering using the pill should discuss the benefits and risks with her GP based on her individual situation.
Further studies will continue to build on our understanding of breast cancer and its causes.