While locally-irradiated MCA/129 fibrosarcomas implanted in asmase−/− mice did not display significant endothelial apoptosis at 4–10 h after 15 Gy (Fig. 5B; P>0.05 at all times vs. control), restitution of ASMase expression with Ad5H2E-PPE1(3x)-ASMase restored endothelial apoptosis to 27±2% at 8 h respectively post 15 Gy (P<0.005 vs. unirradiated control), without evidence of tumor cell apoptosis (<2%). This evidence concerns the gene SMPD1 and fibrosarcoma.