For instance, in breast and lung cancer, inflammatory cytokines, such as IFN-α and tumor necrosis factor (TNF), activate signal transducer and activator of transcription 1 (STAT1) and NF-κB/p65 in brain metastatic cells in response to stimulation by carcinoma–astrocyte gap junctions composed of protocadherin 7 and connexin 43, leading to tumor growth and chemoresistance (31). Here, STAT1 is linked to lung cancer.