I knew that without any study being done. As a provider, I specialize in hormone balancing for women and men. What is worrisome is the large number of young women being placed on contraceptives for many years consecutively. There are many studies indicating that the progestin (synthetic progesterone) part of birth control formulations greatly increase the risk of proliferative breast cancer. Progestins are dramatically different from our natural progesterone and do not "fit" on the cell receptor perfectly well, as our natural hormones do. In fact, they increase estrogen sensitivity instead of policing it and keeping estrogen effects in check, as our natural progesterone would do. There is a belief that breast cancer is caused by hormones- this is not exactly true. Hormonal imbalances, or SYNTHETIC hormones (like in birth control) do contribute to more rapid proliferation of a breast cancer cell once it is formed. Breast cancer cells occur because of environmental exposures, genetics, dietary deficiencies and stress. Our body's natural progesterone actually aids in preventing cancer proliferation by a process called apoptosis, or ridding the body of old and damaged cells. Progestins do not offer this protective effect. It makes complete sense that by altering the molecular structure of a hormone, you will see different effects than what the initial hormone was. I feel women need to be more educated on this, and use birth control very very judiciously. Also, I would completely recommend avoidance of third generation progestins (like in Yaz, Yazmin, or the Nuva Ring) because the risk dramatically higher. This is very disconcerting, since a large majority of young women are on these very brands! Pharmaceutical companies do not want awareness of these risks to spread, because they would lose a great deal of money. These are a professional's recommendations. For more information, I encourage you to read Dr. John Lee's works, or Dr. Uzzi Reis, or Dr. D Zava