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What kid hasn't run around at night capturing fireflies in a jar? Most don't think about what makes them glow, they're just excited and having fun.

But scientists are taking that excitement to new levels, by examining the gene that allows fireflies to flash and using it to track the effectiveness of anti-cancer drugs.

Researchers need to monitor how a tumor grows, divides and metastasizes and to what parts of the body they are spreading, explains Dr. Ralph Mason, Associate Professor of Radiology at the University of Texas Southwestern Medical Center at Dallas.

In animal research, cancerous tumor cells are inserted into a mouse, and then the firefly gene is injected into the body and becomes part of the cell as it divides. Mason and his team are among the first to show that a technique called bioluminescence imaging (BLI) (the conversion of chemical energy into light in living organisms) can be used to determine the effectiveness of cancer drugs that choke off a tumor's blood supply.

"You can plant a tumor on the mouse and measure it with a ruler," says Mason, who also is Principle Investigator of UT-Southwestern's Small Animal Imaging Research Program and Director of the Cancer Imaging Program. "But many tumors grow deep inside the animal, so a ruler is not appropriate. Twenty or 30 years ago, we realized that a firefly gene could be introduced into a tumor cell. Being part of the genome, every time it divides, the tumor will glow. The more light there is, the bigger the tumor. We can use it as quite a robust method. We can do prostate, liver, brain without cutting. We can see if the tumor spreads; metastasis kills the patient, few die from the original tumor."