Cancer pain could be considerably alleviated by blocking a specific type of hormone-like molecule produced by tumours, German scientists say.
The team showed that the molecules make nerve endings grow in nearby tissue, causing an acute sensation of pain.
The molecules highlighted in the study were known to play a role in the development of blood cells in the bone marrow.
But this is the first time they have also been shown to have a role in causing pain. The findings of the Heidelberg University team are published in Nature Medicine.
Pain is one of the most debilitating symptoms associated with the many forms of the disease.
It can become excruciating as cancer advances, but tackling it has proved difficult for doctors.
The researchers hope their work could lead to new drugs to block this action.
Dr Mark Matfield is scientific adviser to the Association for International Cancer Research, which partly funded the work.
He said: "Identifying one of the ways in which cancer causes pain - in fact, perhaps the main mechanism - is a crucial step towards drugs that could bring relief to cancer sufferers across the world."
Dr Joanna Owens, of the charity Cancer Research UK, said: "It's important that we continue to improve pain relief for people with cancer, and this study reveals an intriguing new avenue to explore.
"What's particularly encouraging is that this research could one day lead to drugs that can block pain locally at the tumour site - which could ultimately lead to more effective pain relief with fewer side effects."