STAT1 and neoplasm: Furthermore, brain metastatic tumor cells can deliver the second messenger cGAMP (cyclic GMP-AMP) to astrocytes via gap junctions, thereby activating the STAT1 (signal transducer and activator of transcription 1) and nuclear factor kappa B (NF-κB) signaling pathways within tumor cells through a series of cascades.232 These two signaling pathways are intimately associated with the growth, proliferation, and survival of tumor cells.225,233