Prostate Cancer 'Cell of Origin' Identified

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For researchers, a key to studying any cancer is finding its "cell of origin." Now scientists at the University of California at Los Angeles say they've found just that -- a specific type of cell that gives rise to prostate cancer.

For years doctors worked under the assumption that prostate cancer arose from cells called luminal cells, which line the inside of the prostate's tiny ducts and secrete the prostate gland's fluid.

But by using a new method to grow human tissue in mice, researchers have found a new origin of prostate cancer – a type of cell called basal cells, which support the luminal cells and regenerate prostate tissue.

Cancer experts say the discovery may lead to better treatments in the future.

"Just because something looks like a luminal cell, doesn't mean it's a luminal cell," said Owen Witte, of the UCLA Broad Stem Cell Research Center and lead author of the study published today in the journal Science.

The finding was surprising, because cells in most prostate tumors look similar to luminal cells.

"The basal cells, we've almost always ignored, and it turns out it may be causing cancer," said Dr. Anthony Smith, chairman of the public media committee for the American Urological Association, who was not involved in the study.

Using a new mouse-human model for research

Witte had noticed basal cells were giving rise to tumors in his previous research with mice, so he and his colleagues decided to test the idea in human cells.

The researchers embedded two samples of human prostate tissue into mice -- one sample of the prostate's luminal cells, and the other of prostate basal cells.

Both sets of cells were genetically altered to induce cancer. But, as the human cells lived inside the mice, researchers saw that only the basal cells turned into tumors with luminal-like appearances. The luminal cells did not turn into tumors at all.

Until now, cancer researchers say they were limited to implanting small tumors in mice and studying how they continue to grow. But observing this transformation – from healthy cells into tumors – could help doctors fight many types of cancers at their earliest stages.

"What it will help us do is to pin down the sequence of steps that take you from normal cells to cancer. That's a very different type of model. That is what I think is so significant," said Smith, who is also professor and chief of the division of urology at the University of New Mexico in Albuquerque.

If doctors know the steps that lead to the development of cancer, then "you can intervene at the earliest point," Smith told LiveScience.

Fighting severe prostate cancer

Prostate cancer is the second most common cause of cancer death in the United States after lung cancer.

According to the American Cancer Society, 217,730 new cases will be diagnosed and 32,050 men are expected to die from the disease in 2010. Yet for the majority of men who are diagnosed, prostate cancer will be well managed.

"If you look at men with the most common form of prostate cancer, which is treated locally or with surgery, the five-year survival is 100 percent," said Mark Rubin, professor in pathology and laboratory medicine at New York-Presbyterian Hospital/Weill Cornell Medical Center in New York City, who was not involved in the current study.

However, while many men survive, the minority of men who have severe prostate cancer have few treatment options. "Important, but yet-to-be-proven" results like Witte's may one day help doctors develop new treatments, Rubin said.

"We're not really trying to find more local cancers or early cancers, but we are trying to figure out why some men get aggressive cancers, and those are the men who are dying from the disease," Rubin said. "This is very convincing data, and very exciting results."

Rubin and Smith pointed out the findings are still preliminary.

"Anytime you're dealing with a mouse study, [which is] is what this is, you're very, very early in the process," Smith said.

In addition to possibly unlocking small clues about tumor formation, Witte said the research and methods used could be applied to other cancer types.

"We're now broadly applying this idea of tissue regeneration as a way of studying cancer in other cancer systems," Witte said. "I think it's more of a discovery tool pointing us in a new direction."

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