Today's cancer drugs are notorious for killing healthy cells along with cancerous ones. A new anticancer approach could offer a more precise option: kill just the tumor by choking off its blood supplies. The first drugs based on this approach are now in human trials and, if they work, could provide a virtually side-effect-free means of fighting a host of cancers.

Called vascular targeting agents or antivascular therapies, the new drugs block the blood vessels that carry oxygen and nutrients to tumors. "Basically, it starves the tumor cells to death, so you get a massive amount of tumor-cell kill," says Dai Chaplin, chief scientific officer at Watertown, MA-based Oxigene. This is in contrast to conventional chemotherapies, which kill cancer cells directly, and to another experimental approach called "anti-angiogenesis," in which drugs stop new tumor blood vessels from growing.