A blood test may help diagnose brain cancer up to five years before symptoms arise, an advance that could lead to more effective treatments for the disease, a new study has found.

Interactions among proteins that relay information from one immune cell to another are weakened in the blood of brain cancer patients within five years before the cancer is diagnosed, said lead researcher Judith Schwartzbaum from Ohio State University in the US.

That information could one day lead to earlier diagnosis of brain cancer, said Schwartzbaum, an associate professor at Ohio State's Comprehensive Cancer Centre.

The study, published in the journal PLOS ONE, focused on gliomas, which make up about 80 per cent of brain cancer diagnoses. Average survival time for the most common type of glioma is 14 months.

Symptoms vary and include headaches, memory loss, personality changes, blurred vision and difficulty speaking. On average, the cancer is diagnosed three months after the onset of symptoms and when tumours are typically advanced.

"It is important to identify the early stages of tumour development if we hope to intervene more effectively," Schwartzbaum said.

"If you understand those early steps, maybe you can design treatments to block further tumour growth," she said.

While widespread blood testing of people without symptoms of this rare tumour would be impractical, this research could pave the way for techniques to identify brain cancer earlier and allow for more-effective treatment, Schwartzbaum said.

Schwartzbaum evaluated blood samples from 974 people, half of whom went on to receive a brain-cancer diagnosis in the years after their blood was drawn.

Schwartzbaum was interested in the role of cytokines, proteins that communicate with one another and with immune cells to spark immune responses.

She evaluated 277 cytokines in the blood samples and found less cytokine interaction in the blood of people who developed cancer.

"There was a clear weakening of those interactions in the group who developed brain cancer and it is possible this plays a role in tumour growth and development," Schwartzbaum said.

Cytokine activity in cancer is especially important to understand because it can play a good-guy role in terms of fighting tumour development, but it also can play a villain and support a tumour by suppressing the immune system, she said.