Although the role of PPARγ in tumor progression and metastasis remains controversial, in part because of the potential off target effects of PPARγ ligands (197), consistent with the important role of lipogenesis in breast cancer progression, recent studies showed that genetic deletion of Pparγ1 delayed the onset of tumorigenesis by mammary epithelial cell targeted ErbB2 (198). The gene discussed is PPARG; the disease is breast carcinoma.