In this seminar, Dr Howell will talk about his group’s work in developing breast cancer preventive therapies, in particular with anti-progestins, and will present their new data, currently under revision for publication, on the effects of the anti-progestin ulipristal acetate on the normal breast of women at increased risk of breast cancer. Anti-progestin therapy induces changes in the epithelial hierarchy but more impressively in extracellular matrix composition and stiffness with implications for reduction in breast density and risk.