The risk of breast cancer continues to be higher among women who use or have recently used today’s hormone contraceptives than women who have never used them, a study shows.
It showed that a new generation of the contraceptives have done nothing to lower the risk.
The research, “Contemporary Hormonal Contraception and the Risk of Breast Cancer,” was published in the New England Journal of Medicine.
An estimated 140 million women worldwide use hormone contraceptives. They can be delivered in a number of ways besides birth control pills.
The female hormones estrogen and progestin prevent ovulation, or the release of eggs needed for pregnancy. But estrogen, which is used in pills, promotes the development of breast cancer.
Previous studies showed a correlation between oral contraceptives and breast cancer risk. Scientists studied the link between the two when estrogen doses in contraceptives were higher, however.
Among today’s hormone contraceptives are new forms of progestin treatments and hormone injections. There are also uterine implants that release progestin or another hormone, levonorgestrel, and vaginal rings and skin patches that release hormones.
Because there has been little research on the risk of breast cancer in women who use modern forms of birth control, a Danish research team decided to do a 10-year study of 1.8 million between the ages of 15 and 49. They used a nationwide registry that included information on women’s use of hormone contraceptives and whether they developed breast cancer.
The key finding surprised them. It was that the breast cancer risk of women who were using hormone contraceptives, or had used them recently, was 20 percent higher than in women who had never used them.
“We did actually expect we would find a smaller increase in risk because today we have lower doses of estrogen in the hormone contraceptives, so it was surprising that we found this association,” Dr. Lina S. Mørch, a senior researcher at the University of Copenhagen, said in a press release. She was the paper’s lead author.
The risk varied with the length of hormone contraception use. It was 9 percent higher in women who had used the contraceptives less than a year and 38 percent higher in those who had used them more than 10 years.
When women who had used hormone contraceptives for five years or more stopped using them, their risk of breast cancer was still higher than in women who had never used them.
Interestingly, researchers found that the higher risk applied not just to women using birth control pills but also to women with hormone-releasing uterine implants. In fact, women who used a progestin shield were at 21 percent higher risk of developing breast cancer than women not using it. This suggested that progestin can contribute to the development of breast cancer.
When looking at absolute numbers, for every 100,000 women, hormone contraceptives cause an additional 13 breast cancer cases per year. The figures are 55 cases for every 100,000 women not using hormone contraceptives, versus 68 for those who do.
The study’s bottom line was that today’s hormone contraceptives pose the same risk of breast cancer as the old ones.
“Nothing is risk-free, and hormonal contraceptives are not an exception to that rule,” said Dr. Øjvind Lidegaard, the paper’s senior author. He said doctors should discuss the advantages and disadvantages of different types of contraception with their patients.
The American College of Obstetricians and Gynecologists said it will evaluate the findings, but added that hormone contraceptives are “among the most safe, effective and accessible [birth control] options available.”