When the DNA sensor cGAS detects cytoplasmic double-stranded DNA (dsDNA) released by dead cells, tumor cells or pathogens and mitochondrial DNA (mtDNA) leaking into the cytoplasm, cGAS catalyzes ATP and GTP synthesis of the second messenger 2',3'-cGAMP and directly activates the STING protein in the endoplasmic reticulum. This evidence concerns the gene CGAS and neoplasm.