A few years ago we reported about a landmark Danish study that tracked over 1 million women under the age of 50 in Denmark. While that study has continued and trails have been updated, new research from that follow up group has show that birth control can increase a woman’s risk of breast cancer by up to 38%, depending on how long she has taken it. The risk was associated with all forms of hormonal contraception — such as the pill, injections or IUDs — when compared with women who have never used.
The full article and research links can be found here: https://www.nytimes.com/2017/12/06/health/birth-control-breast-cancer-hormones.html
The study was published in NEJM: http://www.nejm.org/doi/full/10.1056/NEJMoa1700732