Distinguishing between an aggressive form of prostate cancer and a milder case can be a life-or-death proposition. Now researchers have identified a biomarker that they say flag such aggressive tumors.

The discovery, by University of Michigan cancer specialists, could be a potentially important breakthrough in diagnosing and treating prostate cancer. The biomarker could help doctors determine which patients would benefit most from life-saving surgery, radiation, or other agressive therapies and those who can simply keep a close eye on their cancer — “watchful waiting” — to be sure it doesn’t spread to other parts of the body.

Biomarkers in the body are analogous to the warning lights in cars that signal something might need repairing, the researchers said.

"There's a big interest in trying to find biomarkers to discriminate between aggressive and nonaggressive disease [in prostate cancer]," said Renny Franceschi, a UM professor of dentistry, biological chemistry, and biomedical engineering.

Franceschi noted prostate cancer can grow so slowly that men who have it often die of natural causes unrelated to the cancer. But some forms of the disease progress very rapidly are life threatening.

The UM team was able to determine that a protein known as Runx2 activates specific genes in both bone and prostate cancer cells and may there be used to flag aggressive tumors that require immediate treatment, such as surgical removal of the glad.

"If this biomarker does indeed control the growth of prostate cells, it's a new signal that's not been seen before and could provide a potential new drug target for prostate cancer," Franceschi said. "It could also be a potential biomarker to discriminate between fast and slow growing tumors."

Prostate cancer is the second-most common cancer in men, striking 221,000 men and causing roughly 27,500 deaths in the U.S. each year.