15-keto-Prostaglandin E2 is an endogenous bioactive metabolite that inhibits STAT3 activation through covalent interaction with the Cys259 residue, while also binding to and stabilizing EP2 and EP4 receptors, thereby exerting inhibitory effects on breast cancer cell growth and tumor progression, activating PPAR-γ signaling, and promoting fungal growth, collectively positioning this lipid mediator as a multifunctional regulator in cancer biology, immunometabolism, and host–pathogen interaction research.