It's dichloroacetate and it's been used for years to treat metabolic disorders.
New Scientist magazine reports that a team from the University of Alberta has found that DCA has an astounding effect on many cancers, including lung, breast and brain cancers. Best of all, there's no patent on it so it can be produced cheaply.
DCA is said to defeat cancer cells by switching off their immortality but doesn't affect healthy cells and has been proven to be "relatively" safe.
The explanation of just how DCA works is a bit complex so I've included a link to the New Scientist article.