WASHINGTON (Reuters) - A new type of imaging compound can literally light up spreading cancer cells and may offer a way to track the deadly spread of the disease, Japanese and U.S. researchers reported on Sunday.

Molecular imaging of ovarian tumors is seen in this undated handout photo released on December 7, 2008. The activatable probe, right, clearly visualized cancer foci. The control probe, left, also accumulated into the cancer foci, but clear delineation was difficult. REUTERS/Hisataka Kobayashi/Handout

They used the new compound to monitor the spread of breast and ovarian cancer cells in living mice, using a tiny camera known as an endoscope.

“These compounds may allow clinicians to monitor a patient’s response to cancer therapy by allowing them to visualize whether a drug hits its target and whether hitting the target leads to shrinkage of the tumor,” Dr. Hisataka Kobayashi of the U.S. National Cancer Institute, who helped lead the study, said in a statement.

Kobayashi and Yasuteru Urano of the University of Tokyo first targeted breast cancer cells with a certain mutation in what is known as the epidermal growth factor receptor or EGFR, which drives several different cancers.

This mutation is targeted by Genentech’s breast cancer drug Herceptin, known generically as trastuzumab.

The researchers made their imaging compound by linking a fluorescent compound to Herceptin, which is itself a genetically engineered antibody that homes in on cells with mutated EGFR.

It only attaches to living cells, making it possible to specifically find living cancer cells.

Sure enough, they could see breast tumors in living mice, and tumor cells after they spread away from the initial tumor site, they reported in the journal Nature Medicine.

Using another cancer drug, Roche AG’s Zenapax, known generically as daclizumab, and an endoscope, they imaged ovarian cancer tumors that had spread inside the abdominal cavity of living mice.

“Our design concept is very versatile and can be used to detect many types of cancer,” said Kobayashi.

“Unlike other activatable fluorescent compounds, our compound consists of a targeting agent and a fluorescing agent that act independently. We can target the fluorescing agent to different types of cancer cells by using any antibody or molecule that is internalized by the targeted cells after it binds to the cell’s surface proteins.”

Half an hour after they killed the cells, the red fluorescent light stopped, they said.