Furthermore, in the same study, when PARP-1KO mice were crossed to O6-methylguanine-DNA methyltransferase (MGMT) null mice hypersensitive to AOM, double mutants (Parp-1−/−/Mgmt−/−) developed more but smaller tumors compared to the single mutants (Mgmt−/−), suggesting that PARP-1 has a double faced role in colorectal carcinogenesis by suppressing tumor initiation dependent on MGMT following DNA alkylation but promoting tumor progression. Here, MGMT is linked to neoplasm.