Phase II study of dacarbazine for metastatic colorectal cancer: Final results with MGMT analysis.

3581 Background: O6-methylguanine-DNA-methyltransferase (MGMT) is a DNA repair protein removing mutagenic and cytotoxic adducts from O6-guanine in DNA. Approximately 40% of colorectal cancers (CRCs) display MGMT deficiency due to promoter hypermethylation leading to silencing of the gene. Alkylating agents, such as dacarbazine, exert their antitumor activity by DNA methylation at the O6–guanine site, inducing base pair mismatch, therefore activity of dacarbazine could be enhanced in CRCs lacking MGMT. We conducted a phase II study with dacarbazine in CRCs who had failed standard therapies (oxaliplatin, irinotecan, fluoropyrimidines, and cetuximab or panitumumab if KRAS wild type). Methods: All patients had tumor tissue assessed for MGMT as promoter hypermethylation in double-blind for treatment outcome. Patients received dacarbazine 250 mg/m2 i.v. qd for 4 consecutive days q21 until PD or intolerable toxicity. We employed a Simon two-stage design to determinate if the ORR would be ≥ 10%. Secondary endpoin...