Getting Closer to the Origins of Prostate Cancer
Newly discovered stem cell, common STD could help spur tumors, studies find
WEDNESDAY, Sept. 9, 2009 (HealthDay News) -- Two studies take significant steps toward solving major mysteries about prostate cancer -- the exact spot in the gland where tumors can originate, and how to distinguish fast-growing malignancies that are life-threatening from the slower-growing kind that can safely be left alone.
One study, reported in the Sept. 9 online edition of Nature, describes a previously unknown form of prostate stem cell that can become cancerous if genetic controls go haywire. The prostate consists of several layers of cells, with the lowest, the basal layer, playing a supporting role and the luminal layer, just above it, doing the actual work of the gland.
"Up until our paper, it was thought that all the stem cells in the prostate reside in the basal layer," explained study co-author Cory Abate-Shen, a professor of urology, pathology and cell biology at Columbia University's Herbert Irving Comprehensive Cancer Center, in New York City. "We have found a second stem cell population that is luminal rather than basal."
The discovery was made in mice, and the next step is to show that the same kind of stem cells exist in humans. "But this work partially explains how you can have a prostate cancer that is luminal," Abate-Shen said.
The research group already is looking for similar stem cells in human prostate glands. "If we can identify them in humans, we can analyze them molecularly," Abate-Shen said. "We want to do battle with these stem cells."
The mouse work showed that the newly described stem cells can give rise to cancers if the action of a tumor-suppressing gene is lost. That gene is frequently mutated in human prostate cancers.
If the same kind of stem cells are found in human prostate glands, "that would give us a tool to study where and how prostate cancer originates," Abate-Shen said.
The second report, published online Sept. 9 in the Journal of the National Cancer Institute, uncovered an association between infection with a sexually transmitted parasite, Trichomonas vaginalis, and an increased risk of prostate cancer, especially the virulent form of the disease.
"We found an association between serological evidence of Trichomonas infection and prostate cancers that were either advanced at diagnosis or after follow-up proved to be fatal," said lead researcher Jennifer Rider Stark, a postdoctoral fellow at the Harvard School of Public Health.
The finding came from a study that compared 673 men in the long-running Physicians Health Study who had prostate cancer against an equal number of cancer-free participants. A blood test showing infection with the parasite indicated a statistically significant incidence of cancers that were potentially deadly because they spread out of the prostate gland.
Women are routinely screened for T. vaginalis, but men aren't, Rider Stark said. "We often only find out if a man is infected if his female partner has symptoms," she said. "Then we also can treat the male population."
It is possible that screening men for the infection and treating it when it is discovered could reduce the risk of life-threatening prostate cancer, she said. "But it is premature to assume that," Stark said. "We need more population-based studies to confirm that the association actually exists. Until other studies also demonstrate the same association, such measures are a way down the road."
Still, "it's exciting to find a risk factor that is potentially important for prevention," Stark said.
Both findings follow a widely reported study, released earlier this week in the Proceedings of the National Academy of Sciences, that found that a virus called XMRV is strongly related to the more aggressive form of prostate cancer.
Learn about prostate cancer from the U.S. National Cancer Institute.