IDO1 and neoplasm: By incorporating multi-omics analyses, we identified that abnormally upregulated Indoleamine 2,3 dioxygenase-1(IDO1) expression in cancer cells altered tryptophan metabolism, facilitating the release of l-kynurenine (L-kyn)-enriched EVs acquired from the tumor tissues and plasma in OC, which were further validated by larger clinical samples and extra experiments.