The association of Wnt activation with stem cell expansion,activation of β-catenin/TCF signaling by PDK1, the identification of PPARδ as aβ-catenin/TCF target gene and PDK1 as a PPARδ responsive gene, as well as themodulation of Sca-1+ stem/progenitor cells by the Wnt pathway, allsuggest a common mechanism for the tumor promoting action of PPARδ agoniststhat may involve stem and progenitor cell proliferation (see Figure 3). This evidence concerns the gene HNF4A and neoplasm.