Cancer cells can invade their surrounding tissues and spread – or metastasise – to other parts of the body. Once this happens, cancer is much more difficult to successfully treat. In fact, it is estimated that around 9 out of 10 cancer deaths are due to cancer that has spread.
Recently, the advent of new, cutting-edge technologies has allowed scientists to make movies of tiny cancer cells in living tissues. This has flung open the door to studying metastasis by enabling scientists to ‘watch’ how tumours grow and spread. And it generated considerable excitement amongst delegates at the NCRI Cancer Conference this year.
Growing along the tracks
Professor Peter Friedl from Nijmegen Medical Center in the Netherlands presented his eloquent experiments looking at the edges of sarcomas in mice as they grow. His exciting results challenge the conventional idea that it’s single cancer cells that break away from the original tumour and invade the surrounding tissues.
Instead, his movies show there are long strands of connected cells sprouting out of the primary tumour, which grow along pre-existing blood or lymph vessels – the “tracks of least resistance”.
It appears that the growth of these strands is really well-organised. The cells at the bottom all multiply at the same time, pushing the rest of the tip forward through the tissue. And they can move at an incredible one-fifth of a millimetre each day. That may not sound like much, but it’s pretty speedy in cellular terms, translating into a distance of centimetres over weeks or months.
Here’s a short video of cancer cells growing and spreading from Professor Friedl’s lab, taken down a microscope using time-lapse photography. You can see the cancer cells (the cluster in the lower lefthand side) moving like a slug along the underlying lymph vessels along grayish collagen matrix after explantation of the tumour from a patient (squamous cell carcinoma) :
What about human cancers?
The big question, as far as cancer treatment goes, is whether these strands also occur in human sarcomas. Although they’ve never been reported before, Professor Friedl confirmed that a pathologist had taken a much closer look and seen similar strands at the edges of human sarcomas, suggesting that it may be a universal property of these cancers.
At the end of the session, Professor Friedl also hinted that his most recent experiments looking at carcinomas – a type of tumour which makes up about 85 per cent of all cancers – showed that they too behave in a similar way. This means his results – and their implications – could be far-reaching.
This is an exciting new discovery and much more research will be needed to understand what’s happening. But what does it mean for cancer treatment?
Firstly, if these ‘invisible’ strands are penetrating deep into surrounding healthy tissues along blood or lymph vessels, it could have big implications about how much tissue surgeons need to remove from around a tumour.
And their existence could also have an impact on other forms of cancer treatment. Professor Friedl showed that remnants of the strands can survive after radiotherapy, meaning that the cancer can grow back over time.
So if drugs could be developed to kill these growing strands, these could be given alongside radiotherapy to improve the long-term effectiveness of this mainstay cancer treatment.
We still have a lot to learn about how cancers infiltrate and spread into the surrounding tissue. But the rewards will be large, as currently there aren’t any drugs available for patients that effectively target these processes.
And it’s only by carrying out important fundamental biological research that we’ll find ways to develop new treatments to stop cancer in its tracks. This cutting-edge area of research has the potential to revolutionise treatment for many people with cancer in the future.
Alison Ross, Senior Science Information Officer, Cancer Research UK