PCNA and breast cancer: Copper‐based nanoparticles derived from Eucalyptus globulus and quercetin‐loaded CuO‐ChNPs have both demonstrated p53‐mediated apoptosis in breast cancer cells, driven by ROS generation, mitochondrial depolarization, cytochrome c release, and caspase activation, alongside reduced PCNA expression and tumor proliferation in vivo [71, 72].