SMAD6 and breast cancer: More specifically, we identified genes that encode proteins which are critical for cell adherence to the epithelial basement membrane: ITGB1, ITGB6, RHOB, a putative tumor suppressor also commonly mutated in BC 7, 20, MMP7; (Fig 2G); the extracellular matrix organization LOXL2, LOXL4 and TIMP4, an epigenetically silenced putative tumor suppressor in bladder carcinoma 33, and epithelial development and differentiation (SMAD6, SOX2, EREG, WNT11, BMP2).