 Eligible patients will have a diagnosis of colorectal cancer, and will be candidates to adjuvant chemotherapy or first-line chemotherapy for metastatic disease with a regimen containing fluorouracil, capecitabine andor irinotecan. Eligible chemotherapy regimens include Irinotecan, Leucovorin folinic acid, and FluorouracilIFL, Leucovorin, Fluorouracil, and Irinotecan FOLFIRI, combinations of Irinotecan and Capecitabine, the Roswell Park regimen and the Mayo Clinic regimen, all of them without or with Oxaliplatin, Bevacizumab or Cetuximab. Patients receiving Erlotinib, or other Tyrosine-kinase, Epidermal Growth Factor Receptor EGFR-inhibitors, will not be eligible. 