ERBB2 and cancer: In this context, contrasting data are reported on the role of PPARγ as tumor suppressor, since it has been reported that antagonizing PPARγ signaling decreases cancer stem cell population in Erb-B2 receptor tyrosine kinase 2/human epidermal growth factor receptor 2 (ERBB2/HER2)-positive human breast cancer and inhibits tumor formation in an animal model [34], whereas PPARγ downregulation has been associated with Wnt/β-catenin upregulation that is a crucial regulator of stem cells, stem progenitors and cell self-renewal [35,36].