Most people think of cancer cells as foreign invaders that spring up to attack the body.
But the reality is that cancer cells exist surrounded by normal cells and scientists have long puzzled at how the cells can simultaneously co-exist in a seemingly co-operative environment.
Now, a group of Canadian researchers believe that they have figured it out.
"We've known for a long time that there's a dialogue between the cancer cells and normal cells," said Dr. Jeff Wrana, a senior investigator at the Samuel Lunenfeld Research Institute of Mount Sinai Hospital in Toronto.
"But, until now, we thought it was just a few words – some simple signals," he said.
But in the new research, published on Thursday in the scientific journal Cell, Dr. Wrana and his team show that the dialogue is much more complex – "not just words, but paragraphs."
The cancer cells don't attack the normal cells, but rather they entice them to behave badly, to send signals back to the cancerous cells to spread – a process known as metastasis.
Dr. Wrana said that, even more important, this conversation is taking place outside cells, in tiny cell fragments called exosomes.
Exosomes, which are made of proteins, RNA and lipids, were long thought to be cell waste, but they are now understood to be key to intercellular communication. Cells in cancerous tumours, for example, secrete exosomes to help cancer spread.
Further, the research team identified one protein, dubbed Cd81, that is particularly belligerent, meaning that it is really effective at getting cancer cells to spread, especially in the breast-cancer cells they studied.
This knowledge means that, instead of trying to kill tumours, as has traditionally been done when a person is diagnosed with cancer, treatments could be developed to target healthy cells.
"We hope to use our new knowledge of the tumour's immediate surroundings to intercept its signals to cancer cells and, by doing so, dramatically impede tumour spreading," said Valbona Luga, a PhD student in Dr. Wrana's lab and co-author of the study.
"Instead of only targeting the primary tumour, we can now pinpoint the cells in the tumour's environment that are responding to the tumour and target those too, " she said.
In other words, the hope is that drugs can be developed that prevent cancerous cells from sending out their messages – a bit like cutting the phone lines.
Dr. Wrana said work is being done on drug development, but results are many years away. "It's really hard to predict timing," he said.
The new findings, however, may have some practical use in the more immediate future.
That is because the Cd81 protein that the research team identified as being key to the spread of cancer can be used as a marker for aggressive tumours.
By looking for Cd81 signals, oncologists would be able to identify more aggressive breast-cancer tumours and make them a priority for treatment.
The new research also involved scientists from the University of Guelph and Jewish General Hospital in Montreal. It was funded by the Terry Fox Research Institute and the Canadian Institutes for Health Research.