To investigate the contribution of host STING to the anti-tumor efficacy of PARPi plus a STING agonist in Brca1-deficient breast tumors, we employed STING−/− mice (Tmem173gt/gt, C57BL/6J) and EO771 murine breast cancer cells, a syngeneic mouse model on C57BL/6 background. Here, BRCA1 is linked to breast carcinoma.