Dose-Dense Temozolomide in Patients with MGMT-Silenced Chemorefractory Colorectal Cancer

Background: In a phase II study, we showed that temozolomide (TMZ) was tolerable and active in heavily pre-treated patients with advanced colorectal cancer (CRC) and MGMT methylation. A schedule of dose-dense TMZ may have enhanced activity due to the higher cumulative dose and induction of MGMT depletion, even in resistant tumors. Methods: Thirty-two patients with chemorefractory MGMT-methylated CRC were treated with TMZ at a daily dose of 75 mg/m2 for 21 consecutive days every 4 weeks, for up to six cycles or until the occurrence of progressive disease/unacceptable toxicity. The primary endpoint was treatment activity in terms of objective response rate (ORR). MGMT protein expression was tested by immunohistochemistry (IHC) on two pooled cohorts: patients from the previous study of standard-dose TMZ and those from the current investigation. Results: From November 2013 to December 2014, 32 patients were treated at Fondazione IRCCS Istituto Nazionale dei Tumori. We observed only three episodes of grade 3 asthenia and no significant myelotoxicity. The ORR was 16 % (all partial responses occurring in RAS-BRAF-mutated tumors). Median progression-free survival (PFS) and overall survival (OS) were 2.3 and 6.7 months, respectively. Patients with MGMT-low expression by IHC had a significantly higher ORR (p < 0.0001) and PFS (p = 0.001) compared to those with MGMT-high expression, while no difference was observed in OS. Conclusions: Our data confirm the encouraging activity of TMZ in chemorefractory CRC patients selected for MGMT silencing, even in the RAS-BRAF-mutated population. The role of MGMT IHC as a biomarker for improving patient selection warrants further prospective confirmation.[MediaObject not available: see fulltext.]