Engaging the vascular component of the tumor response.

Recent research has shed new light on the critical role of tissue microvasculature in regulating the tumor response to radiation and drugs. In this issue of Cancer Cell, Moeller et al.(2005) demonstrate that HIF-1 activation during the course of fractionated radiotherapy initiates pleiotropic adaptive responses in both tumor cells and the microvascular network, radiosensitizing tumor cells but concomitantly conferring tumor radioresistance due to protection of the microvascular endothelium. HIF-1 thus serves as a legitimate target for differential modulation of tissue response to radiation.