Itga1−/− mice, deficient for the collagen-binding integrin α1β1, show a normal vascular development and a reduced tumor angiogenesis in adulthood, which has been attributed to increased MMP activity [131], while α2β1-deficient Itga2−/− mice show an enhanced tumor angiogenesis in adulthood, but an otherwise normal vascular development [131, 132], and integrin α2β1 is involved in the PlGF-dependent regulation of VEGFR-1 [132]. Here, PGF is linked to neoplasm.