More recently, it has been shown that pre-operative “window” administration of twice daily 100 mg doxycycline for 14 days to newly diagnosed breast cancer patients was effective in reducing the breast cancer stem cell population (measured by both CD44 and ALDH1) [40], suggesting it may provide more clinical benefit in prevention of metastases as opposed to treatment of metastases. This evidence concerns the gene CD44 and breast carcinoma.