"It provides additional evidence that tumors are angiogenesis-dependent, evidence for which has been piling up for 30 years now," Folkman said.

Folkman said the findings suggest a new way to treat tumors that were thought to be untreatable because they were resistant to traditional chemotherapy drug treatments.

He said some angiogenesis inhibitors are currently in clinical trials and may be added to conventional chemotherapy treatments in clinical studies when and if they are approved by the Food and Drug Administration.

The results of the study are particularly important to Folkman and members of his laboratory team, who have been studying angiogenesis for about 30 years.

In 1995, Browder, who was working full-time in Folkman's laboratory, began experimenting with non-standard treatment regimens that utilized a standard chemotherapy drug, Cytoxan. He eventually developed a treatment schedule that appeared to inhibit the regeneration of endothelial cells--the cells that line blood vessels--in test mice.

The treatment schedule consisted of a lower total dose of drugs administered continually every six days.

Conventional chemotherapy treatment typically gives patients high doses of toxic drugs to kill cancer cells and then prescribes a recovery period in which no drugs are administered.