The National Cancer Institute has a nice summary of the relationship between oral contraceptives and cancer, based on several reports. While there were some conflicting results, there seemed to be a consensus that there is a mild increase in the risk of breast cancer among women using oral contraceptives.
Here are the three reports:
- Burkman et al. (2004): This is a general overview of studies done since the first oral contraceptives became widely used, in the 1960s. Data indicates that there is a slightly higher risk of breast cancer among women taking oral contraceptives.
- Hunter et al. (2010): Data was complied from biannual screenings of over 116,00 women over a twelve-year period. It was found that the use of oral contraceptives in the past did not contribute to breast cancer, while the current use of these contraceptives led to a slight increase in risk. However, this focused on a specific type of oral contraceptive.
- Lancet (1996): Over 150,000 women from 54 studies were analyzed. There were three main findings:
- There is a slight increase in breast cancer risk in those who stop taking oral contraceptives after using them regularly for a long time.
- Breast cancers in women using these contraceptives was detected or diagnosed at any earlier stage.
- Women who used contraceptives before the age of twenty had a slightly higher risk of breast cancer.
There are, of course, other studies not mentioned in the NCI article, including these two:
- Heikkinen et al. (2015): The use of general exogenous hormones in oral contraceptives and in hormone-releasing intrauterine devices. In these cases, a slightly higher risk of breast cancer was observed.
- Jordan et al. (2015): This used statistics to estimate cases of breast cancer caused by the use of oral contraceptives. The result was that about 100 cases in Australia in 2010 can be attributed to the use of these contraceptives.
- Zhong et al. (2015): This search of PubMed combined with data analysis methods suggested that there is no link between oral contraceptives and breast cancer.
These three studies have all been published (or even only submitted to PubMed) extremely recently, so their results are not necessarily confirmed by other studies. However, they are certainly more recent than some of the other studies.
There appears to be a slight increase in the risk of breast cancer in women who use oral contraceptives - including the types used today. However, this risk is very, very tiny, and the benefits of contraceptives far outweigh any possible risks in this regard. The results of Jordan et al. (2015), if definitive, should show that any real-world effects are negligible when looked at in the big picture.