MMP13 and breast cancer: One of them, by using a similar approach to studying the role of Pit1, a POU class 1 homeobox 1 transcription factor, revealed that it regulates MMP13 expression in human breast cancer cells and that MMP13 knock-down blocks cancer cell invasion into the lungs, suggesting that MMP13 is a mediator of Pit1 induction of breast cancer lung metastasis [56].