Target practice: figuring out which, when, and why to use systemic therapies for metastatic colon cancer.

There have been many recent advances in the field of systemic chemotherapy for metastatic colorectal cancer. Each treatment affects a different target, including thymidylate synthase, topoisomerase, DNA, the epidermal growth factor receptor, and vascular endothelial growth factor. These treatments have been used in multiple combinations, schedules, and as first-line, second-line, and third-line therapies. The current clinical trials reported can help guide the clinician to determine the appropriate timing, combination, and schedule of chemotherapy agents. Although the decision regarding colorectal cancer chemotherapy is now more complicated, our patients have certainly benefited from better response rates and most importantly, longer survival times.