The study, published in the New England Journal of Medicine, followed 1.8 million Danish women for more than a decade. Researchers concluded that for every 100,000 women using hormonal birth control, there are 68 cases of breast cancer annually, compared with 55 cases a year among nonusers. They note that there's a 20% higher risk of developing breast cancer among women currently or recently using the pill or hormonal IUDs. The longer women used these contraceptives, the higher their risk. Specifically, the risk was 9% for women using it for less than a year to 38% for those using them for 10 years or more.