Irinotecan (Camptosar, CPT-11), a member of the camptothecin family, represents the most active camptothecin available for clinical use today. Irinotecan is a topoisomerase I inhibitor. Topoisomerase enzymes support the topologic structure of DNA, thus facilitating translation and transcription. The enzyme topoisomerase I plays a crucial role in the relegation of single-strand breaks and in relieving torsional DNA stress.[1,2] Irinotecan and other camptothecin analogs interfere in this process by stabilizing the topoisomerase I/DNA cleavable complex.[2] This process is not compatible with prolonged cell survival.