Although it has been reported that activation of PPARγ maintained cancer stem cell properties in ErbB2-positive breast cancer cells [68], a large body of evidence has shown that PPARγ hinders tumor development and progression, in most cases through modulation of differentiation, proliferation, apoptosis and motility of cancer cells via a variety of molecular pathways [18,19,20,21]. This evidence concerns the gene PPARG and breast cancer.