['Advanced hepatoblastoma often is lethal despite current therapies, yet development of novel approaches has been hampered by the lack of biologically relevant models. One new strategy selectively targets endothelium rather than tumor cells using frequently administered, low-dose ("metronome") chemotherapy. Metronome topotecan has antiangiogenic activity in some experimental tumors. The authors developed a xenograft model of human hepatoblastoma to test the effect of metronome topotecan in this system.', 'Xenografts resulted from intrarenal injection of cultured human hepatoblastoma cells in athymic mice. Topotecan (0.36 mg/kg/dose) or vehicle was injected intraperitoneally 5 times per week. At week 6, 10 control/treated mice were killed, and remaining animals were maintained without treatment until week 8. Tumor weights were compared by Kruskal-Wallis analysis, and vascular alterations were ascertained by specific immunostaining.', 'Metronome topotecan affected tumor weights in a delayed fashion: weights were diminished significantly only at 8 weeks (treated v control: 6 weeks, 0.59 g v 82 g, P value, not significant; 8 weeks, 1.13 g v 3.82; P <.02). Decreased vascularity and increased endothelial cell apoptosis were observed in treated xenografts.'] Is topotecan anti-angiogenic in experimental hepatoblastoma?