The new study may resolve this conundrum because the newly discovered adult stem cells are also luminal cells. "Previous research suggested that prostate cancer originates from basal stem cells, and that during cancer formation these cells differentiate into luminal cells," said Dr. Shen. "Instead, CARNs may represent a luminal origin for prostate cancer."

And indeed, the researchers found that CARNs in mice can give rise to prostate cancers, after the cells lose the activity of PTEN, a gene that is frequently mutated in human prostate cancers.

The results do not mean, however, that CARNs give rise to "cancer stem cells," cells inside a tumor that are capable of regenerating the cancer from a single cell. "The relationship between the normal prostate stem cells and potential cancer stem cells is not known yet," said Dr. Shen. "And even the existence of cancer stem cells in prostate tumors is not established."

Also unclear is whether CARNs exist in the normal human prostate and if human prostate cancers originate from these CARNs. Dr. Shen's lab is now looking to investigate these issues.

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