A magnetic method of killing cancer cells has been developed by scientists.
The technique uses a magnetic field to flip a "self-destruct" switch in tumours.
Researchers have demonstrated that the process works in bowel cancer cells and living laboratory fish.
Programmed cell death, or apoptosis, is one of the body's ways of getting rid of old, faulty or infected cells.
In response to certain signals, the doomed cell shrinks and breaks into fragments. These are then engulfed and consumed by amoeba-like immune cells.
Often in cancer, apoptosis fails and cells are allowed to keep dividing uncontrollably.
The magnetic therapy involves creating tiny iron nanoparticles attached to antibodies which bind to "receptor" molecules on tumour cells.
When the magnetic field is applied, the molecules cluster together, automatically triggering the "death signal" that sets off apoptosis.
In laboratory experiments, bowel cancer cells were exposed to the nanoparticles and placed between two magnets.
The cells were designed to light up green to signal that apoptopic clustering was taking place.
More than half the exposed cells were destroyed by magnetic activation, whereas no untreated cells were affected.
In another experiment, magnetically-induced apoptosis in zebra fish caused the creatures to grow abnormal tails.
Details of the research, led by Professor Jinwoo Cheon, from Yonsei University in Seoul, Korea, appear in the journal Nature Materials.
The scientists wrote: "We have demonstrated that apoptosis signalling can be turned on in-vitro (in the laboratory) and in a zebra fish in-vivo (living) model by using a magnetic switch.
"Our magnetic switch may be broadly applicable to any type of surface membrane receptors that exhibit cellular functions on clustering."
The technique may also have applications in regenerative medicine, said the researchers.