Studying triple-negative breast cancer, researchers at Washington University School of Medicine in St Louis found that some aggressive tumours rely on an antiviral pathway that appears to drive inflammation, widely recognised for roles in cancer, rheumatoid arthritis and other inflammatory diseases.
The tumours that activate this particular antiviral pathway always have dysfunctional forms of the proteins p53 and ARF, both encoded by genes known for being highly mutated in various cancers.
The investigators found that the two genes compensate for each other. If both are mutated, the tumours that form are more aggressive than if only one of these genes is lost.
When both genes are lost and the antiviral pathway is activated, patients may benefit from a class of anti-inflammatory drugs called JAK inhibitors, currently prescribed for rheumatoid arthritis.
Until now, even though ARF was known to be expressed in some tumours with mutated p53, ARF largely was thought to be nonfunctional in this scenario.
But the investigators showed that in the absence of p53, ARF actually protects against even more aggressive tumour formation.
"It's probably inaccurate to say that ARF completely replaces p53, which is a robust tumour suppressor with multiple ways of working," said senior author Jason D Weber, associate professor of medicine.
"But it appears the cell has set up a sort of backup system with ARF. It's not surprising that these are the two most highly mutated tumour suppressors in cancer.
"Because they're backing one another up, the most aggressive tumours form when you lose both," Weber said.
Weber and his colleagues studied triple-negative breast cancer because these tumours often show mutations in both p53 and ARF.
The researchers found that most triple-negative tumours lacking p53 and ARF turn on a pathway involved in the innate immune response to viral infection.
"It's not the level of activation you would see in a true antiviral response, but it's higher than normal," Weber said.
"We are interested in studying whether this antiviral response is creating a local environment of inflammation that supports more aggressive tumours," Weber said.
Weber and his colleagues knew that a signalling protein family known as JAK is upstream of the antiviral pathway they showed to be driving tumour growth.
"There are JAK inhibitors in use for rheumatoid arthritis and being tested against a number of other conditions. Our data suggest that these anti-inflammatory drugs may be a way to treat some patients missing both p53 and ARF," Weber said.
The study is published in the journal Cell Reports.