Colorectal cancer is a disease that is curable if detected early and preventable if precursor adenomas are detected and removed. Approximately 130,000 new cases were diagnosed in the United States in 2000, and approximately 56,000 deaths were attributed to the disease. The typical age at which most patients are diagnosed is during the sixth and seventh decades of life [1].
The risk factors for the development of col-orectal cancer include dietary, hereditary, and environmental influences. The activation of protooncogenes and the inactivation of tumor suppressor genes eventually result in the development of malignancy [2]. The adenoma-carcinoma sequence has also been well established. Most colon cancers are thought to develop directly from adenomatous polyps. The cumulative risk for developing invasive carcinoma in unresected polyps is 2.5% at 5 years, 8% at 10 years, and 24% at 20 years [2]. The malignant potential of a polyp is determined by its size. Polyps greater than 2 cm have a greater than 40% risk of being cancerous, whereas those less than 0.5 cm are essentially at no risk for harboring malignancy. Other features of a polyp that predispose to malignancy are villous architecture and degree of cellular atypia and dysplasia [2] (Fig. 1).
Approximately 30% of colorectal cancers occur in the sigmoid, 25% occur in the rectum, and 25% occur in the cecum and ascending colon [2]. The remaining 20% of cancers occur in the transverse and descending colon.