Another important class of pubertal phenotypes is caused by loss- or gain-of-function of matrix remodeling enzymes such as matrix metalloproteinases (MMPs), which regulate ductal invasion and branching via their ability to sculpt the ECM45, 46, and Fgfr1/2 stimulation has been shown to induce the expression of Mmp3 and Mmp9 in several breast cancer and immortalized mammary epithelial cell lines47–51. This evidence concerns the gene MMP3 and breast cancer.