The majority of women who get breast cancer have none of the known risk factors. This tells us that despite all the research that has been done, we still do not know what causes breast cancer or how to prevent it. It also tells us that we need to look more broadly for hints we may have missed in the past. The HOW Study will allow us to search for, and find, these “hidden” risks and gain new insights into what is causing breast cancer. Because we will have a large and diverse cohort of both breast cancer survivors and those who have never had the disease, we will be able to explore both unknown risk factors for the disease and factors that contribute to long-term survivorship.