Methods, systems, and kits for treating breast tissue rely on transferring energy to or from cells lining an individual breast duct. Energy can be introduced into the breast duct, e.g., by filling the duct with an electrically conductive medium and applying radiofrequency energy to the medium. Other energy forms could also be used, such as light, ultrasound, radiation, microwave energy, heat, cold, direct current, and the like. By treating individual breast ducts, cancerous and pre-cancerous conditions originating in the duct can be effectively treated.