In stromal cells, PAEs-induced estrogen-ERα binding upregulates matrix metalloproteinase-2 (MMP-2) and releases transforming growth factor-β (TGF-β), which acts paracrinally on epithelial cells to enhance invasiveness, forming a stroma-epithelium interactive loop potentially associated with cancer promotion and progression (Lee et al., 2014; Yu et al., 2011). Here, MMP2 is linked to cancer.