We anticipated that tumor-located expression of E. coli beta-glucuronidase would more effectively convert SN-38G to SN-38 as compared to viral-mediated expression of murine beta-glucuronidase in tumors [4] since the bacterial enzyme displays about one hundred fold greater catalytic activity as compared to murine beta-glucuronidase [36]. This evidence concerns the gene GUSB and neoplasm.