ALB and breast cancer: In vivo study on an orthotopic BC mouse model (Fig. 2b), which can more closely simulate the natural TME and presence of supporting cells, a large amount of oxygen was in situ generated in tumor tissues after systemic intravenous injection of HSA-MnO2-Ce6 NPs (Fig. 2c), and more complete tumor ablation and longer lifespan in mice than controls was observed after PDT.