Women using some birth control pills, specifically those with high doses of estrogen and a few other formulations, may be at an increased risk of breast cancer, a new study has found. At first glance, the findings seem alarming, but a City of Hope breast cancer surgeon is warning against overreaction.
The study, published recently in the journal Cancer Research and led by researchers at Fred Hutchinson Cancer Research Center in Seattle, compared women who used oral contraceptives in the past year to those who never used them or who had formerly used them. However, the researchers acknowledged, their findings should be interpreted very carefully.
"Our results require confirmation and should be interpreted cautiously,” said study researcher Elisabeth F. Beaber, Ph.D., M.P.H., in a statement released by the journal. “Breast cancer is rare among young women and there are numerous established health benefits associated with oral contraceptive use that must be considered. In addition, prior studies suggest that the increased risk associated with recent oral contraceptive use declines after stopping oral contraceptives.”
The nested case-control study included 1,102 women diagnosed with breast cancer and 21,952 control cases. Recent oral contraceptive use increased breast cancer risk by 50 percent, the researchers found. All study participants were at Group Health Cooperative in the Seattle-Puget Sound area and were diagnosed between 1990 and 2009.
Further, the study found that birth control pills containing high-dose estrogen increased breast risk 2.7 fold, while moderate-dose pills increased risk 1.6 fold. Pills containing ethynodiol diacetate – a steroidal progestin – were also found to elevate risk 2.6 fold. Triphasic combination pills with an average of 0.75 milligrams of norethindrone, a progestogen, more than tripled the risk of developing breast cancer.
Pills with low-dose estrogen were not associated with increased breast cancer risk.
Courtney Vito, M.D., a staff surgeon at City of Hope, said further research on this topic is merited, but women should not get too alarmed as the type of study poses limitations.
"My thoughts, looking at this study, are that perhaps there is some increased risk of breast cancer with certain types of birth control pills. Specifically, it seems to be pills containing moderate to higher-dose estrogen or estrane progestins. Certainly, not all birth control pills have these types of hormones in them. Other types of pills such as those using different types of progesterone or low-dose estrogen did not seem to increase the risk.Vito was also interviewed by HealthDay about the study.
Also, whenever a study is done that is not the gold-standard randomized-controlled trial, there is risk that a bias or difference between the two groups can lead investigators to incorrectly conclude that whatever is being studied is what's causing that difference (in this case, the birth control pills). In this study, the cancer group was more likely to be Caucasian, not have had children and have a first-degree relative (such as a mother or sister) with a history of breast cancer. All of these are known risk factors for breast cancer, and they contribute to the cancer group's risk.
The groups were not balanced, and this was not well-controlled for in the study design. The investigators did not mention whether chart-reviewed patients were pre- or post-menopausal which makes a difference too. Finally, the control group, or those considered to be free of breast cancer, had a larger percentage of women who were not screened for breast cancer by mammogram in the last 18 months which can lead to underdiagnosis of breast cancer in that group.
In summary, I would say that the authors are asking a very important question, and with the limited information available to them in a large population-based retrospective database type study, they give us the suggestion, but definitely not conclusive evidence, that certain types of birth control pills may increase the risk of breast cancer. There are some flaws in this study that are inherent to this type of research, and therefore, further study is merited."
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