SMAD4 and neoplasm: Moreover, human data from the COAD TCGA database revealed that (i) tumours with high RAC1B express lower levels of the apoptotic genes Caspase-3 and -7, (ii) higher expression of RAC1B correlates with fewer mutations within the TGFβ signalling pathway and (iii) a strong negative association exists between SMAD4 mutations and RAC1B expression.