The Pill increases a woman’s risk of breast cancer.
Why? Because oral contraceptives cause a significantly higher rate of breast cell division, and in general, cells that divide more rapidly are more likely to become cancerous.
By how much? According to the 2009 study Risk Factors for Triple-Negative Breast Cancer in Women Under the Age of 45 Years, published in the journal Cancer Epidemiology, Biomarkers, and Prevention, after less than one year of taking oral contraceptives, a woman’s risk of triple-negative breast cancer is increased 2.5 fold.
After more than one year of use, her risk is increased by 4.2 fold. This risk is further increased if a woman begins her use of oral contraceptives before the age of 18, or if she smokes. This increased risk persists for 10 years after ending the use of the Pill.
Triple-negative breast cancer is a particularly aggressive subtype of breast cancer, with little treatment available outside of chemotherapy and mastectomy.