A breakthrough could lead to drugs to alleviate the pain experienced by cancer patients.
The biology of cancer pain is different to other types of pain, often rendering analgesic drugs ineffective.
Work by a German team, published in Nature Medicine, shows that blocking a specific type of hormone-like molecule produced by tumours could help.
The team showed that the molecules make nerve endings grow in nearby tissue, causing an acute sensation of pain.
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 molecules highlighted by the latest study, by a team at Heidelberg University, 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 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."