The issue of whether or not oral birth control pills increase the risk of breast cancer or not, has been confusing and contradictory for at least the last 20 years. It is certainly an ongoing concern in the minds of many women and clinicians. This recent prospective cohort study from the Denmark national data base attempted to determine if there was any association between use of hormonal contraception and risk for invasive breast cancer in women aged 15-49. Approximately 1.8 million women were followed for an average of 10.9 years from 1995-2012. In that period of time, 11,517 breast cancers were diagnosed. Most of the hormonal contraceptives were oral formulations and then secondarily, progestin IUDs. The relative risk for breast cancer in current or recent users of these products was compared to those women who never used hormonal contraception and found to be 1.20 with an absolute risk of 13 additional cases of breast cancer per 100,000 person years. Current or recent use of the progestin IUD was associated with a similar, 1.21 relative risk. Breast cancer was uncommon in women who used contraceptive implants or injections.
Commentary: While the authors of this study adjusted the findings for many things, including duration of hormonal contraceptive use, age, education, parity, polycystic ovary syndrome, endometriosis and a family history of breast or ovarian cancer – What they did not adjust for was clinical breast examinations, screening mammograms and lactation history, all of which are considered potential issues that confound the results. In addition, it must be factored in that > 80% of breast cancers are in women older than 49, and in the current analysis, they limited their aged group to women between 15 and 49.
Researchers consider that a relative risk of less than 2 or 3 should not be interpreted as an indication of causation; so, in this study, with the results of 1.21, it could not be concluded that current or recent use of hormonal contraception was the cause of their breast cancer.
In one of the definitive studies on this topic, conducted by the Centers for Disease Control and published in the New England J of Medicine in 2002, there was no suggestion of an excess risk for breast cancer with use of oral contraceptives.
The current study does indicate the possibility of a very small increase in risk, the best available data on this topic shows that they do not have an impact on the risk of breast cancer. With increased understanding of numerous genes, on breast cancer risk, not just BRCA genes, and an increased attention to the effect of environmental pollutants, it is likely that this is where we should be putting our attention. However, it may also be true that in women who take in particular oral contraceptives, these medications may provide some kind of fertile environment for then an added negative influence from the genetic issues as well as environmental exposures, two areas that currently leave us asking more questions. In the meantime, there are numerous non hormonal options for contraception, and pregnancy is a risky enterprise in and of itself, with medical risks that outpace the POSSIBLE very small increase relative risk of birth control pills and breast cancer.
And don’t forget… there is good published scientific evidence that the following reduce our risk of breast cancer: exercise at least 3.5 hours per week; less alcohol- not more than 7 drinks/week (some data says 0-3/week), avoid overweight/obesity; while the research is not as robust, there is also evidence that we can reduce our risk of breast cancer by eating a Mediterranean diet, getting more sunshine (adequate vitamin D levels), fish and/or fish oil supplements, higher fiber diets, olive oil, and green tea.
Reference:
Morch L, et al. Contemporary hormonal contraception and the risk of breast cancer. NEJM 2017;Dec 7; 377:2228
Hunter D. Oral contraceptives and the small increased risk of breast cancer. NEJM 2017;Dec 7;377:2276
