Scientists have discovered how cancer spreads from a primary site to other places in the body in a finding that could open doors for new ways of treating and preventing advanced disease.
Instead of a cell just breaking off from a tumour and travelling through the bloodstream to another organ where it forms a secondary tumour, or metastasis, researchers in the United States have shown that the cancer sends out envoys to prepare the new site.
Intercepting those envoys or blocking their action with drugs might help in the prevention and treatment of cancer.
"We are basically looking at all the earlier steps that are involved in metastasis that we weren't previously aware of. It is complex, but we are opening the door to all these things that occur before the tumour cell implants itself," said Professor David Lyden, of Cornell University in New York.
Cancer's ability to colonise other organs is what makes the disease so deadly. Once the cancer has spread beyond its original site it is much more difficult to treat.
In research reported in the journal Nature, Professor Lyden and his colleagues describe what happens before the arrival of the cancerous cells at the new site.
"The authors show that tumour cells can mobilise normal bone marrow cells, causing them to migrate to particular regions and change the local environment so as to attract and support a developing metastasis," Patricia Steeg, of the National Cancer Institute in Bethesda, Maryland, said in a commentary.
Cells at the site of the metastasis multiply and produce a protein called fibronectin, which acts like a glue to attract and trap the bone marrow cells to create a landing pad or nest for the cancer cells.
"These nests provide attachment factors for the tumour cells to implant and nurture them. It causes them not only to bind but to proliferate. Once that all takes place we have a fully formed metastatic site or secondary tumour," said Professor Lyden. "This is the first time anyone has discovered what we call the pre-metastatic niche."
Without the landing pad, the cancerous cell could not colonise the organ.
In animal and laboratory studies, the scientists looked at how breast, lung and oesophageal cancer spread. The envoys from the tumour determine the site of the secondary site.
Professor Lyden said measuring the number of special bone marrow cells circulating in the body could help to determine whether a cancer was likely to spread.
THE BIG C
* Cancer kills 7 million people a year.
* Scientists believe smoking, alcohol, obesity, poor diet, unsafe sex and lack of exercise contribute to about a third of all cancer deaths.
* By reducing these risks, people increase their chance of avoiding cancer.