Targeted therapy in colorectal cancer.

Advances in chemotherapeutic agents have led to improved outcomes for patients with metastatic colorectal cancer (CRC). Chemotherapies, however, are limited by their toxicities and lack of specificity. Aberrations in the regulation and expression of growth factors have been implicated in the development of CRC, and this understanding has led to the development of targeted agents. In 2004, two novel agents, bevacizumab and cetuximab, were approved by the US Food and Drug Administration for the treatment of metastatic CRC. Bevacizumab, a humanized monoclonal antibody to vascular endothelial growth factor, and cetuximab, a human-mouse chimeric monoclonal antibody to the epidermal growth factor receptor, have changed the field dramatically. Bevacizumab appears to augment the efficacy of combination chemotherapy regimens for the treatment of metastatic CRC in both the first- and second-line settings, and the role of bevacizumab as part of adjuvant treatment is the subject of ongoing trials. However, because of the increased incidence of serious arterial thromboembolic events, gastrointestinal perforations, bleeding complications, and hypertension associated with bevacizumab, this agent is probably not indicated in all circumstances. Combination treatment with cetuximab and irinotecan appears appropriate in patients with advanced CRC who have failed irinotecan. Patients who are unable to receive additional irinotecan may be treated with cetuximab monotherapy. Positive epidermal growth factor receptor status by immunohistochemistry of a tumor specimen is presently mandated to determine candidacy for this therapy, although this assay appears to be suboptimal and newer assessment techniques to determine suitability for therapy must be developed. Phase III trials should shed light on the role of cetuximab in the first-line metastatic and adjuvant settings. Multitargeted strategies in CRC combining chemotherapy with bevacizumab and cetuximab are currently being explored. Further advances in the treatment of CRC are expected through continued scientific investigation and well-designed clinical trials.