Cell lines deficient in PTEN have an impaired homologous DNA recombination and increased cytotoxicity with PARP1 inhibition both in vitro and in vivo An estimated 50% of breast cancers, irrespective of their triple-receptor negativity, have a mutation in, or loss of, at least one copy of the PTEN gene [83,84]. Here, PTEN is linked to breast carcinoma.