Molecular evidence for this clinical correlation was provided by Zhang et al. in a mouse model of breast cancer, showing that binding of collagen I to the cell surface receptor discoidin domain receptor 2 (DDR2), a receptor tyrosine kinase, leads to the formation of collagen fibers oriented perpendicular to the surface of the tumor, facilitating cells invading out along these (75). Here, DDR2 is linked to breast carcinoma.