The natural hormone levels in the blood affect the risk of breast cancer. At their turn, these hormone levels are determined by genetic, reproductive, lifestyle, and professional risk factors and hormone use.
As a better understanding of these risk factors will give clues for prevention and will improve risk prediction, we initiated several prospective national cohort studies among Dutch women: the Hereditary Breast and Ovarian cancer study Netherlands (HEBON), the Nightingale study and the DESnet cohort.