Studies on the link between the use of oral contraceptives (OC) and breast cancer continue to give a mixed picture, i.e., some studies show a correlation and some studies do not. Much of the mixed results are due to the multifaceted nature of breast cancer, the age of initiation, length, and type of OCs used, whether OCs were used before the first birth, whether there is a familial/genetic risk, lifestyle factors, how many pregnancies brought to live birth, how many abortions, and whether the women breastfeed or not and the length of breastfeeding. The quality and methodology of the research is also another reason for the mixed results, especially when comparison groups are not randomized (which is difficult or impossible to do with such a study).
In any case, the first generation of OC users from the 1960s and early 70s usually initiated use of OCs after the birth of their first child and at a later age. This pattern of use has changed radically over time with now many teenage girls initiating use at a young age and continuing until their first child at a much later date. Many women are now continuously on OCs for 10 or more years. A case controlled study in Finland was conducted to determine whether women who initiated the use of OCs at a young age and before their first child have an increased risk for breast cancer.1 There were 37,153 recorded cases of breast cancer among Finnish students born between 1946 and 1960. For each of these cancer cases they randomly selected 5 aged-matched controls that did not have cancer. Of these cases, those who used the Helsinki Student Health Service at least three times yielded 150 cases with breast cancer and 316 control subjects for final analysis. The reason that the researchers used those who attended the student health services is that they were able to obtain records that detail the use of OCs.
The results showed that women who had used OCs had a statistically higher risk for breast cancer (the adjusted odds ratio was 2.1) than those few women who never used OCs. However, the researchers were not able to find a statistically higher risk among women who started OCs at a young age compared to those who were older at initiation of use and there was no difference in the risk between those who started OCs before their first birth and those who started after. The main reason there were no differences is that there were too few subjects who started OCs before 20 or who did not use OCs before their first birth. The authors concluded that the impact of early initiation of OCs cannot be answered until around the year 2010 when those women who wereborn after the 1960s are in their 40s and 50s. These women will more likely reflect the early use of OCs than the previous generation of OC users.
The Finnish researchers were only able to find 15 cases who never used OCs among the breast cancer group and 57 among the control group. The fact that they could find so few women who have never used OCs makes this type of research more difficult to detect significant differences.
1 Hernminki, E., Luostarinen, T., & Pukkala, E., et al. Oral contraceptive use before first birth and risk of breast cancer: a case control study. BMC Women's Health. 2002;2:9 (http://www.biomedcentral.com/1472-6874/2/9) [Back]