STING1 and cancer: Cancer cells can transfer cGAMP to astrocytes via the cancer-astrocyte gap junction channel, which activates STING in astrocytes and subsequently produces inflammatory cytokines such as IFN-α and TNF-α, which in turn activate signal transducers and activator of transcription 1 (STAT1) and NF-κB signaling pathways in the cancer cell, leading to brain metastasis (45).