At this point, the nanocarriers only target tumors' blood vessels, so they can't image or attack tumors without vasculature. This includes most tumors smaller than about two cubic millimeters. But Gao says tumors in the dangerous process of spreading, or metastasizing, are large, have well-established vessels, and can be directly attacked.

And unlike other targeted cancer therapies, he adds, the nanocarriers are easy to modify. As researchers discover more targets unique to cancer cells, the nanocarriers can be equipped to find, image, and destroy other types of cells within tumors and also different types of cancer, he says. He is now working on a system that directly targets lung-cancer cells.

The clearer images created by nanoparticles delivered directly into cancer cells could ultimately allow many new possibilities, says Michael Bonder, a postdoctoral researcher at the University of Delaware's Cancer Translational Research Center. Doctors could detect smaller tumors and possibly watch them metastasize, or spread cell by cell to new parts of the body.

But toxicity remains a risk, even with the targeted nanocarriers, cautions Glen Kwon, associate professor of pharmaceutics at the University of Wisconsin. He says Gao's team should run tests to ensure that minimal amounts of the drug leak out as the nanocarriers travel through the bloodstream. "This is often a major challenge for nanocarrier systems in drug delivery," Kwon says.

Patrick Winter, assistant professor of medicine at Washington University in St. Louis, adds that it's questionable how many nanocarriers will reach their target. "Even the best targeting strategies" only get a small fraction of the nanocarriers into the tumor, and the rest end up in normal tissues, he says. No matter how well the new nanocarriers perform, some will likely end up in "clearance organs like the liver and spleen," which "could lead to side effects," he says.

Gao counters that so few nanocarriers will be injected that even if a large fraction missed their target, no side effects would occur.

But the new nanocarriers are promising as "a triple threat to a cancer cell," says Robert Sikes, director of the Laboratory for Cancer Ontogeny and Therapeutics at the University of Delaware. "They seek out, display the location, and deliver the lethal blow to dividing cancer cells," he says.