biosystems) was performed. The siRNA targeting of Smad4 (Ambion:ID5365) was performed. SP cell were isolated from each pancreatic cancer cell line. TGF-β treatment significantly reduced SP cell frequencies and enhanced the effects of Gemcitabine. SP cell with TGF-β treatment survived better than non-SP cell. KP1N and KP1NL cell were derived from the same parental cell line and their responses to TGF-β treatment were opposite. It revealed growth inhibition in SP cell of KP1NL, whereas growth-promotion in KP1N cell. Using DNA-microarray analysis we identified the 50 genes differentially expressed gene between KP1N and KP1NL. Quantitative Real-time PCR revealed obvious change in. Leftright-axis determination gene Lefty. DNA array analysis and real-time PCR analysis revealed more than 50 times higher expressions in TGF-β treated group. We found that Smad4 downregulation by siRNA administration un-expectedly increased Lefty expressions. Lefty was induced by TGF-β in SP cell of Pancreatic cancer cell. This up-regulation of Lefty was not directly controlled by Smad4 cascade. Lefty could work as an effecter of TGF-β and as a tumor suppressor in pancreatic cancer.