SMAD2 and triple-negative breast carcinoma: Unlike in mice, where Smad2 deficiency is embryonic lethal [46] and Smad3 deficient mice are viable and fertile [47], Smad3-deficiency in MDA-MB-231 triple negative breast cancer cells retarded their growth similar to TMEPAI knockdown [14, 15] and Smad2 deficient cells behaved like wildtype cells (Figure 2).