Histochemical evaluation of the liver, kidney or pancreatic tissues collected from 7 week old tumor bearing mice 7 days following administration of a single dose of STA-12-8666 or an equivalent dose of irinotecan demonstrated significantly lower incidence of pS139-H2AX-positive nuclei (indicative of DNA-damage response [28]) in the STA-12-8666-treated animals in comparison to the irinotecan group in keeping with the established tissue toxicity of SN-38 (Figure 2B, Supplementary Figure S1). The gene discussed is H2AX; the disease is neoplasm.