Tumor markers in colorectal cancer: Predictors of risk

Despite many advances, colorectal carcinoma remains a significant cause for death in the United States, in part because of delayed diagnosis and in part because of disease recurrence. Tumor markers offer potential to improve cancer therapy in a number of ways including: early detection of primary tumors; prediction of tumor behavior and response to treatment; monitoring responses to treatment; early detection of recurrences; and, more recently, diagnosis of genetic predisposition. In broad terms, there are three main categories of tumor markers: (1) tumor associated antigens, such as carcinoembryonic antigen and carbohydrate antigen 19-9; (2) markers of cellular proliferation, such as DNA ploidy and proliferative index; and (3) genetic markers, such as alterations in oncogenes and tumor-suppressor genes. This article discusses each category of tumor marker, with emphasis given to their roles in disease prognosis and monitoring response to treatment.