PCDH7 and carcinoma: Chen et al. [90] reported that in order to metastasize to the brain, breast and lung cancer cells establish carcinoma-astrocyte gap junctions and use the connexin 43 (Cx43) channels and PCDH7 neuronal receptors to transfer the second messenger cGAMP to astrocytes to create a favorable environment (i.e., a niche) for carcinoma cells to grow by activating their STAT1 and NF-κB survival signals [90].