<qa>  What is the name of the enzyme that can enhance the efficacy of iriRationale: Previous studies suggest that both irinotecan and Mytomycin C when administered alone have some efficacy against stomach cancer. Based on laboratory testing, researchers hypothesized that Mytomycin C may enhance the efficacy of irinotecan through an enzyme called Topoisomerase I. In addition, because Mytomycin C has severe side effects, combining these chemotherapy agents together may allow for lower dosages resulting in greater efficacy and reduced side effects. A recent study indicates that the combination of these drugs has promising anti-tumor activity against esophageal and stomach cancers. The current study builds on previous research to explore the most effective schedule for administering these drugs together. 