Rates of proliferation detected using Ki-67 immunohistochemistry demonstrated no significant changes across all treatment cohorts in ASMase−/− mice (0 Gy, 28.0±1.4% of the tumour cells stained for Ki-67; 10 Gy/5F, 25.1±3.3%; 20 Gy/5F, 18.8±1.6%; USMB only, 22.6±2.2%; 10 Gy/5F+USMB, 25.2±1.3%; 20 Gy/5F+ USMB, 27.4±2.5%), with the exception of the 20 Gy/5F group showing a decrease in proliferation rates compared to those of the 0 Gy (P<0.002) and 20 Gy/5F+USMB (P<0.05) cohorts (Fig. 6A,B). This evidence concerns the gene MKI67 and neoplasm.