Adult stem cells have been touted for their promise in regenerative medicine. But there is no clinical reason to regrow a prostate, says Leisa Johnson, a senior scientist at Genentech and coauthor of the Nature paper. The vast majority of prostate-cancer patients are beyond their child-bearing years, and the main side effects of prostate removal--urinary incontinence and impotence--are caused by nerve disruption during surgery, so they wouldn't be remedied by a new prostate.

Even so, says Jacks, the newly isolated prostate stem cells may provide insight into adult stem cells in general. "Our understanding of stem cells--and adult stem cells in particular--might allow us to re-create damaged tissues that are lost during debilitating diseases," he says.

More important, however, the stem cells may have much to reveal about prostate cancer. Only a small number of cells in a tumor actually have the capacity to spawn an entire tumor, with all its various cell types. Many researchers speculate that these cells, dubbed cancer stem cells or cancer-initiating cells, have much in common with normal adult stem cells. Some even suspect that cancer stem cells and normal stem cells are one and the same.

"We now believe that for many types of cancer, the cell that gives rise to the cancer in the normal tissue is itself a stem cell," says Jacks. "If that is true for prostate cancer, then having the ability to purify and therefore study the normal stem cell would be an important tool in understanding how prostate cancer originates."

Johnson agrees. "By gaining insights into the normal stem cell of the prostate, our hope is to gain better understanding of the cancer-initiating cell," she says.

If it does turn out that stem cells, or stemlike cells, are responsible for triggering prostate cancer, markers like c-kit may also point the way to potential treatments. Now that the Genentech researchers have a pool of definitive prostate stem cells on hand, they can revise the catalogue of known prostate stem-cell markers and even begin to define their function. If any markers turn out to be essential for stem-cell proliferation, they would be ideal drug targets.

Characterizing the newly discovered prostate stem cells may also produce better ways to detect prostate cancer. "These cells could easily turn out to be the cells of origin for prostate cancer," says Jacks, "and if you're interested in early detection, it is important to understand where these cancers come from."