For example, PARP inhibition was shown to synergize with: (1) PI3K pathway antagonism in BRCA-proficient triple-negative breast cancer cells, (2) ATR–Chk1 inhibition in PARPi-resistant BRCA-deficient cancer cells and high-grade serous ovarian cancer cells, (3) BET inhibition in multiple tumor lineages, (4) VEGFR antagonism in ovarian cancer cells. This evidence concerns the gene CHEK1 and cancer.