The Effect of Oral Contraceptives on the Incidence of Breast Cancer

Background: The use of oral contraceptives (OCs) is very popular and widespread, as at least 100 million women worldwide use them, not only for birth control, but also for many other purposes. The safety of OCs has been thoroughly examined, and a great number of studies have been conducted to investigate the correlation between OC use and breast cancer, but with conflicting conclusions. Aim: Review of the correlation found between OC intake and the risk of breast cancer in a wide agerange of women who took the pill either during the observation time or before. Method: Search of the electronic databases Cochrane library, PubMed, Medline, and Google Scholar, using the key words: “contraceptives”, “oral”, “cancer”, “breast”, “risk”, “hormones”, revealed 69 relevant primary studies. The inclusion criteria for this review were: (a) Papers published in the English language, (b) papers that refer solely to the specific breast cancer type and the specific kind of hormone treatment, (c) exclusion of studies that included cancer induction risk factors, such as the genetic factor BRCA 1,2, and (d) papers published between 1990 and 2010. Only 30 studies ultimately met the inclusion criteria. Results: A linear correlation between duration of OK intake and breast cancer incidence was identified by a small number of studies. The age of first OC use was found to be slightly correlated with breast cancer incidence in some studies, but others showed opposite results. Concerning correlation between the OC dose or type of hormones used and breast cancer incidence, it has been shown that women aged 20-44 years that used OCs containing >35 μg of ethinyl oestradiol had an approximate risk 50% higher than that of non-users (RR=1.99, RR= 1.27, respectively). OCs containing high-dose progestin were related to a higher breast cancer incidence among women aged under 35 years, with RR 8.11. Second generation OCs showed an overall higher risk for breast cancer than the absence of use of OCs. Conclusions: The dosage and type of OC, the age of the woman at first use and the duration of the use all play a role in breast cancer incidence, according to a number of studies, while others failed to demonstrate statistically significant differences between users and non-users. On balance, the results derived from the studies were inconclusive with regard to obtaining a firm connection between OCs and breast cancer incidence. The need for further monitoring is crucial.