A cell that could be the "mother" of all prostate tumours has been identified by scientists.
Samples of the "basal" cells taken from healthy human prostate tissue triggered cancer in mice with suppressed immune systems.
The finding suggests that these cells may be the true culprits behind the disease which kills around 10,000 men a year in the UK.
Previously it was thought that a different type of immature cell, known as a luminal cell, lay at the root of prostate cancer.
Experts hope the discovery, reported in the journal Science, will lead to better diagnostic tools and more effective treatments for the disease.
The US team began by extracting both luminal and basal cells from non-cancerous human prostate tissue samples.
First, the cells were altered by inserting defective genes into them known to trigger cancer. Then they were implanted into susceptible mice with impaired immune systems.
The results showed that it was basal rather than luminal cells that initiated prostate cancer in the animals.
Dr Owen Witte, from the University of California at Los Angeles (UCLA), one of the study's senior authors, said: "Certainly the dominant thought is that human prostate cancer arose from the luminal cells because the cancers had more features resembling luminal cells.
"But we were able to start with a basal cell and induce human prostate cancer and now, as we go forward, this gives us a place to look in understanding the sequence of genetic events that initiates prostate cancer and defining the cell signalling pathways that may be at work fuelling the malignancy, helping us to potentially uncover new targets for therapy."