A new study into how cancer cells spread around the body has revealed that the process may take place much earlier than was previously thought.
Cancer spread, or metastasis, has traditionally been thought of as a late event that only happens when the disease is advanced and has passed certain stages.
However, the new research on mammary cells in mice indicates that metastatic disease could be inherent in apparently normal cells that spread out around the body but remain dormant until they are "switched on".
The US researchers believe that the findings could prompt a complete rethink about metastasis and lead to new ways of tackling the disease. The study could explain why some cancers spread long after the initial tumour has been treated.
The researchers at the Memorial Sloan-Kettering Cancer Centre in New York, writing in the journal Science, said: "These findings indicate that properties inherent in normal cells are sufficient for negotiating a significant portion of the metastatic cascade.
"The finding that metastatic disease can arise from untransformed mammary cells in the circulation refines our conception of cancer progression, and suggests that each step in the metastatic cascade should be examined to establish its functional requirements, including those performed by normal cells."