Cancer cell spread was followed in mice
A technique which literally places a window in a mouse's chest could help scientists unlock cancer's most mysterious and deadly process.
US scientists were able to keep a mouse alive for 21 days with the tiny piece of glass in place.
During that period they could watch cells from a breast tumour as they spread to other tissues, reports the journal Nature Methods.
Cancer Research UK said it could unlock ways to stop this spread in humans.
In many cancers, it is not the initial tumour that kills - the danger rises as bits of it break away and travel to other parts of the body.
However, what triggers this process, called metastasis, is still poorly understood.
This is partly because it is impossible to watch metastasis in action. The behaviour of cancer cells in a laboratory dish may be radically different from their behaviour in living tissue.
The team from the Albert Einstein School of Medicine in New York, has been hunting for ways to allow scientists to view metastasis in the body.
Their earlier attempts involved peeling back a flap of skin on the mouse's chest so that the microscopic activity could be seen directly.
However, metastasis happens over days or even weeks, and the mice could not survive under anaesthetic for this long. In addition, conditions in the open wound were far drier than inside the body.
Their new technique involves inserting the glass "coverslip", which means the mouse can live - and the cancer cells observed - for much longer, with the "micro-environment" surrounding the tumour kept intact.
Then cancer cells were marked with substances which allowed their movements to be tracked under the microscope.
This approach is already reaping its rewards - they found that subtle changes to this "micro-environment" seemed to create the right conditions for cancer cells to begin their journey away to other parts of the body.
Dr Joanna Peak, Cancer Research UK's science information officer, said: "Tackling metastasis remains one of the biggest challenges in successfully treating cancer, but it's also one of the most difficult elements of cancer to study in the laboratory.
"This cutting-edge research provides new opportunities to study the complex relationship between cancer cells and their surrounding tissue - to help us understand metastasis in more detail."