DDR2 and breast cancer: In GEMMs deletion of Ddr2 appears to have a greater impact on breast cancer metastasis than does either α1 or α2 Integrin deletion (two α chains of collagen binding integrins), while β1 Integrin plays a critical role in tumor initiation and maintenance (Lahlou and Muller, 2011) (Ramirez et al., 2011) (White et al., 2004).