Multistage approaches such as Ferrari's are still at an early stage. Robert Langer, a professor of chemical engineering at MIT, calls it a "nice approach," but points to the need to demonstrate its effectiveness in animals and clinical trials. Other experts disagree whether silicon will be an effective delivery material. James Baker, a physician and professor of biologic nanotechnology at the University of Michigan, says stiff, microscopic particles will likely be trapped in narrow blood vessels. But Michael Sailor, a professor of chemistry and biochemistry at the University of California at San Diego and another leader in the field of multistage delivery, says that silicon particles could be injected close to the tumor, eliminating the need for them to travel through the bloodstream.

If successful, the relatively large microscopic carrier particles could be used as a generic transport for a variety of combinations of drugs and nanoparticles selected for specific types of tumors. This approach could also make it possible to use drugs that have been dismissed for being too easily degraded in the body or too toxic to deliver using conventional approaches. "It is an attack that holds much promise," says James Tour, a professor of chemistry at Rice University who hopes this approach could be used to deliver some of the tumor-targeting nanoparticles he is developing. "It's not a sure win, but there is cautious optimism."