STING1 and breast cancer: Some studies have shown that tumor cells can selectively degrade extracellular cGAMP through the production of ectonucleotide pyrophosphatase-phosphodiesterase 1 (ENPP1), thereby preventing its transfer from cancer cells to immune cells and promoting tumor metastasis.223 In breast cancer, the inhibition of ENPP1 successfully suppressed tumor metastasis.224 However, evidence also exists that suggests the cGAS-STING pathway can promote metastasis.