Although at molecular levels, MPH inhibits PARP1/2 2-4-fold less potently than the approved PARP inhibitor AZD2281, it causes 2.58-fold more potent in vitro proliferative inhibition than the latter in HR-deficient cancer cells and approximately equipotent in vivo growth inhibition in HR-deficient xenografts. This evidence concerns the gene PARP1 and cancer.