PARP1 and breast cancer: Cells that lack functional BRCA1 or BRCA2 are sensitive to PARP inhibition; thus, PARPi are useful agents in the treatment of BC patients with germline mutations in DNA repair genes, particularly those with deleterious BRCA1 and BRCA2 mutations, which constitutes 3–4% of all women with breast cancer and includes 10–20% of those with TNBC [233].