Researchers from the University of Liverpool found that the protein is made by the PRKCZ gene, which has previously been shown to play a role in aggressive prostate cancer.
One version of the gene produced a protein only made in prostate cancer cells, according to the scientist who believe it could be used as a disease marker, and provide a potential new target for drug treatment.
"We've identified a sequence of the PRKCZ gene in prostate cancer cells that is expressed independently from the normal version, and the protein produced by this gene contains a unique active region," Prof Chris Foster, who led the study, was quoted as saying by the Daily Mail.
"We now need to discover what role this protein is playing in prostate cancer. If it encourages aggressiveness in the disease then we may be able to develop new drugs that reduce its effects," Prof Foster said.
Dr Julie Sharp, from the charity Cancer Research UK which owns the British Journal of Cancer, said: "With more than 40,000 men now diagnosed each year with the disease there's an urgent need to develop tests that tell us how the disease is behaving.
"This research opens a new window on the disease and suggests that versions of this PRKCZ gene could be playing an important role.
"This study highlights how genetically complex cancers are and shows we need to understand and use this knowledge to treat them successfully."
The study is published in the British Journal of Cancer.
