CASP3 and neoplasm: Figure 4A shows immunostaining for cleaved caspase 3 (CC3) in A673 xenografts with a clear increase in the proportion of cells expressing CC3 24 h after RH1 dosing (Figure 4B), although this increase was not maintained at later time points. In 791T osteosarcoma xenografts, however, no increase in percentage of cells with CC3 was observed at two time points (24 and 48 h) after RH1 treatment, although in these cells the background level of apoptosis in sham-treated tumours was relatively high and may have masked any RH1-induced effect (Figure 4B).