STF-1084 is a specific, cell-impermeable, competitive inhibitor of ENPP1 (Ki = 33 nM) . STF-1084 increases extracellular cGAMP concentrations by preventing its degradation by ENPP1, thereby enhancing immune infiltration. STF-1084 acts synergistically with ionizing radiation (IR) and cGAMP to delay tumor progression. STF-1084 can be used to study cancers with low immunogenicity[1].