Inclusion Criteria:  Patients with newly diagnosed stage IV colon or rectal cancer who are RAS/BRAF wild-type by routine tumor profiling and who are beginning standard-of-care treatment with fluorouracil-based doublet chemotherapy in combination with anti-EGFR monoclonal antibodies. Prior treatment with adjuvant therapy is allowed if completed more than 6 months prior to relapse of disease.  Exclusion Criteria:  Pregnant women will be excluded from the study. Patient unable to give informed consent will be excluded from the study. Patients who have previously received chemotherapy in the metastatic setting. Patients who have previously received adjuvant chemotherapy less than 6 months prior to relapse of metastatic disease.