Cancer that has spread throughout a person’s body is tough to kill without causing too much collateral damage. But tiny “protein-factory” particles could target tumors specifically by manufacturing cancer-killing drugs anywhere within the human body.

MIT researchers now have created such tiny particles that could someday make cancer-killing proteins on demand. Such nanoparticles — materials that range roughly in size from 1/1000 to 1/100000 the diameter of a human hair — contain a mixture of biological machinery needed to make proteins based on DNA sequences.