One of the biggest challenges in fighting cancer is stopping metastasis – preventing tumour cells from spreading through the body. Now scientists have identified a promising new way of blocking this growth, and it's shown great results in mice.

A team of researchers in Switzerland have found a "barrier" that stops cancer from metastasising. It's built by a protein called Activin B and a receptor called ALK7 - the combo appears to play a crucial role in stopping tumours in their tracks.

The results of their research so far show that Activin B and ALK7 create a signalling pathway that causes cancer cells to naturally kill themselves off (apoptosis), and prevents tumours from forming (tumorigenesis) and spreading.

While the bulk of the tests so far have only been carried out in mice, we share enough biological and chemical similarities with the furry rodents, especially when it comes to how cancer develops - hence this barrier could be a promising target for cancer-fighting drugs in the future.

"This study enforces the notion that apoptosis is an important barrier of tumorigenesis, and that its evasion by cancer cells is a key hallmark capability of cancer cells during malignancy and metastasis," says one of the team, Douglas Hanahan from the Swiss Federal Institute of Technology Lausanne (EPFL).

For the cancer blocking to work, the receptor ALK7 and the Activin B protein that activates it need to be working in tandem. The researchers found that cancers can suppress ALK7, Activin B, or both in order to survive.

The protein complexes called activins, of which Activin B is one, play a crucial role in many different parts of the body – they're involved in handling the growth and spread of cells, our metabolism, the body's immune response, and the regulation of the menstrual cycle.

The team studied both pancreatic neuroendocrine and breast cancer in mouse models. They went on to look at human patients with various cancers, and found an association between the presence of ALK7 and a lower chance of a relapse.

Metastasis also seemed to be kept at bay for longer when higher levels of ALK7 were present, particularly in cases of breast cancer.

That backs up the idea that ALK7 and its partner Activin B could be useful chemical agents in preventing metastasis, though we're going to need more research before this discovery forms the basis of an actual treatment.

The more ways we have of targeting cancer the better: scientists continue to make good progress in outlining different approaches of attack, from detecting DNA damage more effectively, to stopping abnormal clumps of cells from forming.

ALK7 has tended to go "under the radar" in the past, the team suggests, but we can now add it to our arsenal of potential weapons.

"Elucidating how cancer cells manage to overcome nature's various 'safety checkpoints' to prevent malignancy is an important step towards understanding tumour biology and disease pathogenesis," says one of the researchers, Iacovos Michael from EPFL.

The research has been published in Developmental Cell.