Prospective Study to Identify Molecular Mechanisms of Clinical Resistance to Standard First-line Therapy in Patients With Metastatic Colorectal Cancer

The major obstacle to the cure of cancer by pharmacological agents is resistance to these agents. Clinical responses of metastatic cancers to the most advanced chemotherapeutic agents usually range from 15 to 40%, indicating that intrinsic resistance, and acquired resistance occurs almost inevitably in those tumors that do respond. In patients with metastatic colorectal cancer, clinical resistance to a particular treatment is a clear endpoint (tumor growth), and is usually observed within 6-12 months of any given therapy. Thus, drug resistance and selecting appropriate therapeutic alternatives for drug-resistant cancer remain major dilemmas for oncologists.

The current first-line treatment for metastatic colorectal cancer in Quebec and much of North America is a combination called FOLFOX (the fluoro-pyrimidine 5-FU given as a 46-hour infusion, folinic acid and oxaliplatin) in combination with bevacizumab (Avastin®). An alternative regimen of cytotoxic drugs, also used with Avastin®, is FOLFIRI, which simply replaces oxaliplatin with the topoisomerase inhibitor irinotecan. In the metastatic setting, studies have not demonstrated significant differences between the two regimens, such that decision-making lacks definitive tools.

The objective of this study is to identify, in clinical samples, the molecular signature of clinically resistant colorectal cancer (CRC) patients for the most current and commonly used therapeutic agents. The goals of this study are two-fold. First, to build a biobank of blood and tissue specimens, prior to starting chemotherapy and at a determined time-point (progression of disease), from patients undergoing the same standard and well established first-line treatments (FOLFOX/bevacizumab or FOLFIRI/bevacizumab) for metastatic colorectal cancer. Second, to use state-of-the-art approaches by various collaborating laboratories to correlate clinical outcomes with molecular events that can be used to predict and circumscribe chemoresistance.