Disadvantages of the oral contraceptive pill
A large cohort of studies have shown that women who have used the COC pill are associated with a marginally increased risk of breast cancer (OR=1.15). No strong associations in relation to age started, duration of use, time since first or last use or use related to pregnancy have been observed. This associated risk of developing breast cancer returns to the same level as women who have never used the pill within ten years of last use.
Recently published data sets from the Royal College of General Practitioners’ Oral Contraceptive Study were at odds to this consensus finding, showing no apparent increased incidence of breast cancer with COC pill use. However, a collaborative reanalysis of this data demonstrated a 25% increased risk of breast cancer among its population in a remarkably short exposure of three years, leading to the adjustment of the original results so that they were more consistent with other data sets.
The Women’s Environment, Cancer and Radiation Epidemiology (WECARE) Study found that oral contraceptive use prior or subsequent to a diagnosis of unilateral breast tumour was not associated with the risk of developing asynchronous bilateral breast cancer. Furthermore, studies found neither a harmful or beneficial effect on breast cancer mortality. However, there has been a recent study suggesting that the use of high-dose oestradiol-containing preparations within five years prior to diagnosis may negatively affect survival, but study numbers were small.
There is no evidence that oral contraceptive use among women who carry the BRCA1 or BRCA2 genes confers any greater risk of breast cancer beyond its effect in the general population. However, the duration of COC pill use in relation to the timing of a first full-term pregnancy may increase the incidence of breast cancer in this patient population. (BRCA1 and BRCA2 are breast cancer susceptibility genes. The normal gene plays a role in repairing breaks in DNA, but mutations are thought to disable this repair mechanism, resulting in more DNA replication errors and resultant cancerous growth. People carrying a mutation in this gene are therefore at an increased risk of breast or ovarian cancer.)
Interestingly, a recent paper released from the Norwegian Women and Cancer Study has shown a significant increase in the incidence of breast cancer in women using hormone replacement therapy with a history of COC pill use, compared with women who have never used COC pills (OR=1.67). This may have a significant impact on post-menopausal breast cancer risks as the population of post-menopausal women who have used the pill increases.
The International Agency for Research on Cancer classifies the COC pill as a cause of cervical cancer. Yet there has long been debate as to whether there is a direct causal association between the pill and the disease or an indirect effect relating to changes in sexual behaviour leading to an increase in exposure to carcinogens, primarily the human papillomavirus.
The International Collaboration of Epidemiological Studies of Cervical Cancer recently published results suggesting that, compared with women who have never used COC pills, there was an associated relative risk of cervical cancer of 1.90 in women who use or have previously used oral contraception. The risk has been shown to return to normal within ten years of stopping use. The recent General Practitioners’ collaborative study reported an adjusted risk of 2.73 and is consistent in trend with the World Health Organisation’s collaborative study.
It is estimated that with ten years of COC pill use there is an increase of 7.3–8.3 cases per 1,000 population in less developed countries and an increase of 3.8–4.5 per 1,000 in developed countries. However, it is important to note that many studies have not contextualised the success of national screening programmes.