They also performed real-time PCR to investigate the expression of transcriptional targets regulated by Smad4 and found that expression of p21 and p15, targets of TGF-β and Id3 and Id4, and targets of bone morphogenetic protein (BMP) were inhibited as expected, illustrating the mechanism of how Smad4 targeting by miR-421 affects the cancer cell phenotype. This evidence concerns the gene SMAD4 and cancer.