It has long been known that birth-control pills (oral contraceptives) increased a woman’s risk of getting breast cancer by about 20%. Those data were accumulated during a time when the doses of estrogen and progestin were higher than they are today. Investigators in Denmark decided to re-ask the question in the era of low-dose BCP’s. In the New England Journal of Medicine on December 7, 2017 they published the results of their study. Click here for a copy of the abstract of the article. Dr. Stark can provide a copy of the full article if you fill out the form to the right of this page. For copyright reasons he cannot post it to this website. So what did they find? Basically the 20% increased risk of breast cancer seen with the earlier pills has remained constant. The hoped-for reduction if risk did not occur. Because the sample size was so large the authors were able to do subgroup analysis. Perhaps their most important finding in this regard was the conclusion that the duration of exposure had a powerful impact on risk: the longer you were exposed, the greater the risk. In addition the risk persisted for at least five years after stopping the pill. The authors estimate that there was one extra case of breast cancer for every 7690 women under observation in the study, so the risk is still very small.
In their editorial comments, the authors ask their readers to weigh this increased risk against the known decreased risk of endometrial, ovariand and colorectal cancer in women on the pill. They did no weigh the magnitudes of the increased versus the decreased risk. They also reminded their readers that BCP’s are very effective contraceptives, the reason most women take them.
Dr. Stark comments, Now as in the past in medicine there is no such thing as free lunch. Nonetheless it is reassuring that a woman’s increased risk of breast cancer with BCP’s is modest and may be offset by the good they do.