SMAD4 and exocrine pancreatic carcinoma: As these stably transfected SW480 cell clones express "subphysiological" Smad4 levels (roughly one third of "normal" endogenous levels in Smad4-positive cell lines), we asked if higher Smad4 levels as previously obtained through retroviral gene transfer in Smad4-deficient pancreatic carcinoma cells (i.e. BxPC3) were adequate to overcome the limiting receptor levels in SW480 cells.