IDO1 and cancer: In recent years, ICB therapy has shone brightly in the landscape of precision cancer treatment strategies, particularly for breast cancer.[5] The activating of CD8+ T cell recruitment can provide unprecedented opportunities for the development of immunotherapies for BRCA.[3] IDO1, an endogenous immune inhibitory mediator, stimulates the accumulation of Treg cells and inhibits T cell activity by consuming TRP and accumulating KYN in the TME.