 Irinotecan, a topoisomerase inhibitor, was the first systemic chemotherapy drug other than 5-Fluorouracil 5-FU to demonstrate significant activity in the treatment of metastatic colorectal cancer. Irinotecan is approved for use in combination with 5-FUfolinic acid in patients without prior chemotherapy, and for the second-line treatment of metastatic colorectal cancer as a single agent in patients who have failed an established 5-FU containing treatment regimen. 