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There has been a study (or more than one) that suggest a link between taking oral contraceptives known as the pill and an increased risk of breast cancer.

I have tried find to find the study but my university doesn't seem to have purchased access.

I would like to know how good are the studies suggesting a link? Do they even pertain to today's low dosage version of the pill?

If there is a link between the pill and breast cancer, how does it compare to other health risk due to medication? A fifty percent increase to get it certanly sounds like a lot, but buying two lotto tickets boosts my chances by 100% and who of us has won because of that?

  • My first thought is that at the very least a study into this needs to correct for number of children - having more children is correlated with a lower risk of breast cancer, while being on contraception is of course correlated with having less children. So that might lead to women on contraception seeming to have more breast cancer, while actually, it's not because of the pill itself. – YviDe Oct 18 '15 at 13:45
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+50

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.

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Short answer, there is no definitive link between oral contraception and breast cancer.

You can find a short rundown on the relative risks in this article on Birth Control on Science-Based Medicine.

Information on cancer and oral contraceptives can be found here. There is an increased risk of cervical cancer, but most cases are related to HPV infection, so hopefully the new vaccines will eliminate much of that risk. There is an increased risk of liver cancer in low risk populations but not in high-risk populations. The risk of breast cancer may or may not be slightly increased: studies do not agree.

On the other hand, the pill clearly reduces the risk of uterine and ovarian cancers. And a meta-analysis found that the risk of colorectal cancer is also decreased.

The magnitude of these risks is small. I couldn’t find any information about overall cancer risk: whether the increase in some types of cancer outweighs the decrease in others.

....

[The International Agency for Research on Cancer] does classify estrogen/progesterone in the same group 1 category as cigarettes and asbestos, but all that category means is that there is sufficient evidence to prove carcinogenicity in humans.

  • from the source cited in your source "whereas the risks of breast, cervical, and liver cancer appear to be increased". This is sloppy science! Addendum: Almost the important part is the absolute increase in risk, as illustrated in the example I gave above. – pindakaas Oct 9 '15 at 15:15
  • @pindakaas - If you follow the link to the actual study from that sentence, you find this in the abstract: "...indicate that there is a reduction in the risk of endometrial and ovarian cancer, a possible small increase in the risk for breast and cervical cancer,..." - i.e. a possible, not proven yet, small increase in the risk. And most of these risks disappear over time after stopping use. – JohnP Oct 9 '15 at 15:45
  • @Sean - Your source states, "The risk of breast cancer may or may not be slightly increased: studies do not agree." This does not support your answer. People reading your answer should not have to chase down a link. If you have a better link, please include it. – anongoodnurse Oct 9 '15 at 20:28
  • @anongoodnurse: How do you feel that the lack of evidence doesn't show no definitive link? – Sean Duggan Oct 9 '15 at 22:37

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