The link between estrogens, collagen biosynthesis and degradation, PRODH/POX, PPAR-γ and apoptosis/survival led us to evaluate the impact of estrogen receptor activation on the above processes and PRODH/POX-dependent apoptosis in MCF-7 and MDA-MB-231 breast cancer cells as is outlined on the Scheme 1. Here, ESR1 is linked to breast cancer.