Recently, it has been found by researchers that the hormone Progestin makes cancer cells behave like stem cells- self-renewing, creating identical copies and multiplying exponentially. It was found to considerably increase protein expression of CD44, a molecule involved in cell propagation, cell communication, and movement, leading to the development of cancer stem-cell like cells.
Reference Link: http://www.futurity.org/progestins-breast-cancer-1486472/