Most tumors contain regions of low oxygen concentration where cancer therapies based on the action of reactive oxygen species are ineffective. Now, American scientists have developed a hybrid nanomaterial that releases a free-radical-generating prodrug inside tumor cells upon thermal activation. As they report in the journal Angewandte Chemie, the free radicals destroy the cell components even in oxygen-depleted conditions, causing apoptosis. Delivery, release, and action of the hybrid material can be precisely controlled.