These observations, similar in vitro sensitivity to PARP inhibition of breast and ovarian cancer cell lines, but different clinical efficacy of PARP inhibition in patients with ovarian cancer and BC, allow for the possibility that factors independent of the primary tumor cell type contribute to the effectiveness of PARP inhibition in BRCA1/2-mutant tumors, such as differences in the composition of the tumor microenvironment (TME) and specifically the innate immune system (Kubli et al., 2019; Mehta et al., 2021; Morse et al., 2019). This evidence concerns the gene PARP1 and breast cancer.