PARP1 and cancer: It has recently been discovered that breast, ovarian and prostate cancer cells which carry bi-allelic mutations for breast cancer susceptibility gene (BRCA) 1 or BRCA 2 or that are phosphatase and tensin homolog deficient (and therefore unable to express RAD51), are extremely sensitive to inhibitors of PARPis and to deletion of PARP-1 [1,2].