SMAD4 and neoplasm: Given the preferred association of RAC1b expression in PDAC with cells of an epithelial subtype [16], this suggested the possibility that SMAD4 (and SMAD3) contribute to both maintenance of the epithelial phenotype and tumor suppression and that TAp73 and RAC1b act upstream of these SMADs as part of the same pathway to control their expression (Figure 8).