PET-CT and Circulating Tumor Cells in Colorectal Cancer

1. To determine if measuring both tumor metabolic response (via FDG-PET scan) \& circulating tumor cells (CirTC) at 4 weeks after starting treatment, is a better predictor of clinical outcome than measuring either modality alone in patients with metastatic colorectal cancer (CRC) who are undergoing first-line oxaliplatin-based chemotherapy. 2. To determine if a new method of assessing drug response (measuring tumor metabolic response via FDG-PET \& CirTC at 4 weeks after starting treatment) better predicts clinical outcome than the conventional method (measuring radiological changes in tumor dimensions at 10 weeks after starting treatment via the 'Response Evaluation Criteria in Solid Tumors' - RECIST).