PARP1 and neoplasm: The application of PARP inhibitors in tumors with BRCA mutations blocks both DNA single-strand and double-strand damage repair, the classic synthetic lethal mechanism, whereas in BRCA wild-type tumors, even though PARP inhibitors prevent the repair of DNA single-strand breaks and further DNA double-strand breaks occur, tumor cells can still repair DNA damage due to homologous recombination repair.