Cancer cells were surrounded and destroyed
The fight against cancer could be helped by the discovery of a strain of mice which appear to have the ability to resist the disease.
The mouse immune system launches a massive attack on cancer cells, destroying them.
Tumours that would normally be swiftly fatal to them disappeared within days.
There are no immediate practical benefits to humans - but scientists hope they can find out why the mice are different and harness these differences.
The remarkable strain was noticed by accident by experts at Wake Forest University Baptist Medical Center.
During a routine cancer experiment, a virulent form of the disease was injected in laboratory mice.
They are healthy, cancer-free and have a normal lifespan
Dr Zheng Cui, Wake Forest University Medical Center
In normal circumstances, the tumour expands swiftly, spreading to the liver, pancreas, lung, stomach and intestine.
However, the researchers noticed that one male mouse remained disease free, despite repeated injections of cancer cells.
A colony of 700 mice was bred from this one male - and the resistance to cancer carried on, proving this to be a genetic trait.
Some had complete resistance, with the cancer cells never gaining a foothold, while, in others, the cancer started to develop, but then spontaneously shrivelled away in less than 24 hours.
Dr Zheng Cui, who led the research team, said: "The mice became healthy and immediately resumed normal activities including mating
"They are healthy, cancer-free and have a normal lifespan."
A closer look at the abilities of the mice revealed that the arrival of cancer cells was greeted almost immediately by a massive attack by white blood cells - part of the immune system - which swamped the cancer cells and destroyed them.
Scientists say it demonstrates how important the immune system is in the fight to stop cancer developing.
The Wake Forest researchers said it might show why some people, despite repeated exposure to cancer-causing agents - such as a lifetime of tobacco use - never get lung cancer.
The study was published in the journal Proceedings of the National Academy of Sciences.