The findings of a large study from Denmark were a disappointment for those hoping that women taking or using low dose hormonal birth control (pills, IUD) would not show an increase in breast cancer (like the old higher dose birth control pills). This study found a small increase in the risk of breast cancer with the use of modern birth control pills and with a progestin-only intrauterine device. They pointed out that the biggest risk was in those using hormonal methods for over 10 years and in their 40s (most of the breast cancer cases occurred in this group of women). The risk goes up the longer one uses hormonal contraception.
Due to smaller numbers of women using a birth control patch, vaginal ring, and implants - they were unable to say one way or another if these also are linked to a higher incidence of breast cancer. But the sense from the researchers is that all hormonal contraception has a slight increase in risk of breast cancer. How big an increase in risk? There is a 20% increased risk overall, but the actual numbers are fairly small - 13 per 100,000 women or approximately 1 extra breast cancer for every 7690 women using hormonal contraception for 1 year. From Medical Xpress:
Modern birth control pills that are lower in estrogen have fewer side effects than past oral contraceptives. But a large Danish study suggests that, like older pills, they still modestly raise the risk of breast cancer, especially with long-term use. Researchers found a similar breast cancer risk with the progestin-only intrauterine device, and they couldn't rule out a risk for other hormonal contraceptives like the patch and the implant.
But the overall increased risk was small, amounting to one extra case of breast cancer among 7,700 women using such contraceptives per year. Experts who reviewed the research say women should balance the news against known benefits of the pill - including lowering the risk of other cancers.
Researchers analyzed health records of 1.8 million women, ages 15 to 49, in Denmark where a national health care system allows linking up large databases of prescription histories, cancer diagnoses and other information. Results were published Wednesday in the New England Journal of Medicine. Novo Nordisk Foundation funded the research, but played no role in designing the study.
Current and recent use of hormonal contraceptives was associated with a 20 percent increased risk of breast cancer. Risk increased with longer use, from a 9 percent increase in risk with less than a year of contraceptive use to a 38 percent increase after more than 10 years of use. Digging further, the researchers found no differences among types of birth control pills. Because of fewer users, the results for the patch, vaginal ring, implant and progestin shot were less clear, but the analysis didn't rule out an increased breast cancer risk for those methods. [Original study.]