Cancer cell enzymes shown to act as 'good cops'
Enzymes released by cancerous cells have a protective function and are not one of the "bad guys", say researchers from the University of East Anglia.
Their study found the MMP-8 enzyme sent a signal to the immune system to attack the tumour.
Patients whose breast tumours have more of this enzyme seem to do better.
Cancer Research UK said the research provided "very early clues" as to how the enzyme might recruit cells to fight breast cancer.
Scientists from UEA worked with clinicians at the Norfolk and Norwich University Hospital to look in detail at the patterns of MMPs in breast tumours from patients.
Their study, published in the Journal of Biological Chemistry, reveals that the matrix metalloproteinase-8 enzyme (MMP-8) could be acting as the 'good guy' by alerting the immune system to the location of the tumour.
It had been thought that the production of MMPs by breast cancer cells helped to promote cancer growth.
Prof Dylan Edwards, lead researcher from UEA's School of Biological Sciences, said that if breast cancer cells produce MMP-8 it causes them to produce two other inflammatory factors (IL-6 and IL-8) that have previously been shown to promote cancer.
"They were once thought to act like 'molecular scissors' to snip away at the scaffolding structures outside cells and clear a path for the cancer cells to invade and spread to other organs.
"However, breast tumour cells that over-produce MMP-8 don't survive long-term - the enzyme stops them growing," he said.
"We now think that in tumours, MMP-8 acts as a sort of 'find me' signal to the immune system, which then becomes activated to attack the tumour, which may help to explain its protective function."
Drugs used to treat cancer in the 1990s, which blocked these enzymes, failed in the clinic, he said, and this new research may explain why.
It is still not known exactly how MMP-8 causes IL-6 and IL-8 to be activated.
Finding this out will be an important step forward which will help direct further research.
Dr Emma Smith, senior science information officer at Cancer Research UK, said: "This study provides very early clues as to how the MMP-8 protein might actually play the role of a 'good cop' and recruit immune cells to fight breast cancer.
"And, rather than seeing the MMP-8 protein as a 'bad cop' in breast cancer, recent research has shown that levels of this protein are raised in women who do relatively well.
"Yet, until now, we haven't known why this should be the case.
"But these are early findings from cells grown in a lab, and more research is needed to see if the molecules found by the scientists alert immune cells to cancers in women."