In the the March 11th online edition of PNAS, scientists from Northwestern University Feinberg School of Medicine, L-M Postovit et al., reported their results on studying the role of Lefty and its ability to suppress metastatsis and tumorigenesis in human breast carncinoma and melanoma. Lefty is a protein which appears to regulate pluripotency in embryonic stem cells (ESCs) as well as its ability to suppress the tumorigenic phenotype of cancer cells in an hESC microenvironment. Lefty is an inhibitor of the Nodal signaling pathway (Nodal is a morphogen essential for maintaining pluripotency in ESCs). In a previous study, the authors noted that Lefty was not expressed in metastatic tumor cells. In the current study, it was found that if the tumor cells were exposed to the human ESC microenvironment containing Lefty, there was a marked decrease in Nodal expression "concomitant with a reduction in clonogeniticy and tumorigenicity" in those cancer cells. There was also an increase in apoptosis in the tumor cells. The experimental results also demonstrated that the loss of tumorigenicity was directly correlated with secretion of Lefty in the hESC microenvironment. The authors concluded that neutralizing or inhibiting expression of Nodal or its signaling pathway may provide another therapeutic approach for treating cancer.