Researchers at Cornell University, in the US, attached a cancer-killing protein called Trail, which has already been used in cancer trials, and other sticky proteins to tiny spheres or nanoparticles.
When these sticky spheres were injected into the blood, they latched on to white blood cells.
Tests showed that in the rough and tumble of the bloodstream, the white blood cells would bump into any tumour cells which had broken off the main tumour and were trying to spread.
The resulting contact with the Trail protein then triggered the death of the tumour cells, 'BBC News' reported.
"The data shows a dramatic effect: it's not a slight change in the number of cancer cells," said lead researcher Professor Michael King.
"The results are quite remarkable actually, in human blood and in mice. After two hours of blood flow, they [the tumour cells] have literally disintegrated," he said.
He believes the nanoparticles could be used before surgery or radiotherapy, which can result in tumour cells being shed from the main tumour.
It could also be used in patients with very aggressive tumours to prevent them spreading.
The study was published in Proceedings of the National Academy of Sciences.