Using biologic markers to optimize therapies

5-Fluorouracil (5FU) has been the main treatment of choice in colorectal cancer (CRC) in both the advanced and adjuvant settings for the past 40 years, with response rates of only 10% to 20% in the advanced setting. The combination of 5FU with newer therapies such as oxaliplatin and irinotecan has significantly improved response rates to 40% to 50%. Despite these improvements more than half of advanced CRC patients derive no benefit from treatment, which is due to the development of drug resistance. This review highlights the current prognostic and predictive markers that have been identified for CRC to date and the limitations to their usefulness. Furthermore, we discuss novel targeted therapies for endothelial growth factor receptor and vascular endothelial growth factor. Finally, we focus on the development of microarray analysis to identify panels of predictive markers for CRC, which ultimately aim to tailor treatment according to an individual patient and tumor profile.