TKT and cancer: Although promoter activity and cancer cell specificity of ERE73s-ARF (−13) in DLD-1 cells were less than those observed in 5637 or Soas-2 cells (Figure 2C,D), Ad-ERE73s-ARF-TK was able to inhibit DLD-1 tumor growth in a mouse xenograft model, in the absence of significant side effects, in vivo (Figure 4 and Figure 5).