There are no magic bullets in the fight against cancer: that's the first thing every responsible scientist mentions when discussing a possible new treatment, no matter how promising. If there were a magic bullet, though, it might be something like dichloroacetate, or DCA, a drug that kills cancer cells by exploiting a fundamental weakness found in a wide range of solid tumors. So far, though, it kills them just in test tubes and in rats infected with human cancer cells; it has never been tested against cancer in living human beings. DCA ... is an existing drug whose side effects are well-studied and relatively tolerable. Also, it's a small molecule that might be able to cross the blood-brain barrier to reach otherwise intractable brain tumors. Within days after a technical paper on DCA appeared in the journal Cancer Cell last week, the lead author, Dr. Evangelos Michelakis of the University of Alberta, was deluged with calls and e-mails from prospective patientsto whom he can say only, Hang in there. DCA is a remarkably simple molecule. It acts in the body to promote the activity of the mitochondria. Researchers have assumed that the mitochondria in cancer cells were irreparably damaged. But Michelakis wondered if that was really true. With his colleagues he used DCA to turn back on the mitochondria in cancer cellswhich promptly died. One of the great things about DCA is that it's a simple compound, in the public domain, and could be produced for pennies a dose. But that's also a problem, because big drug companies are unlikely to spend a billion dollars or so on large-scale clinical trials for a compound they can't patent.