Nanotechnology can be used to build assemblies of designed molecules that seek out specific cells - such as cancer cells - but an alternative approach to targeted therapies is to build machinery large enough to be controlled from outside the body, such as the microcarriers demonstrated here: "Soon, drug delivery that precisely targets cancerous cells without exposing the healthy surrounding tissue to the medication's toxic effects will no longer be an oncologist's dream but a medical reality ... sing a magnetic resonance imaging (MRI) system, [researchers] successfully guided microcarriers loaded with a dose of anti-cancer drug through the bloodstream of a living rabbit, right up to a targeted area in the liver, where the drug was successfully administered. This is a medical first that will help improve chemoembolization, a current treatment for liver cancer. ... The therapeutic magnetic microcarriers (TMMCs) [are made] from biodegradable polymer, [measure] 50 micrometers in diameter - just under the breadth of a hair - [and] encapsulate a dose of a therapeutic agent (in this case, doxorubicin) as well as magnetic nanoparticles. Essentially tiny magnets, the nanoparticles are what allow the upgraded MRI system to guide the microcarriers through the blood vessels to the targeted organ. During the experiments, the TMMCs injected into the bloodstream were guided through the hepatic artery to the targeted part of the liver where the drug was progressively released."