IDO1 and neoplasm: For example, STING-dependent DNA sensing enhances tolerogenic states and promotes tumor growth in tumors characterized by low antigenicity via activation of indoleamine 2,3 dioxygenase (IDO) [21]; Moreover, brain metastatic cancer cells can transfer cGAMP to neighboring astrocytes, resulting in activation of the STING pathway and production of inflammatory cytokines such as IFNα and tumor necrosis factor (TNF), which ultimately facilitate tumor metastasis [22].