CASP9 and sarcoma: However, cell death caused by the transduction of dnStat3 appeared to be apoptosis as cleaved caspases 3, 8, and 9 were observed in increased portions of dnStat3-expressing RD2 and U2OS sarcoma cells (Figure 5A, B &5C; cleaved caspase 9 staining for U2OS and cleaved caspase 8 staining for RD2, data not shown).