July 15 (HealthDay News) -- Certain types of circulating blood cells appear to be important predictors of the spread of cancer in children, say French researchers.

They measured levels of circulating endothelial cells and endothelial progenitor cells in 23 children with localized cancer, 22 children with metastatic cancer and 20 healthy children. Circulating endothelial cells are rare cells shed from the lining of blood vessels after vascular damage. Endothelial progenitor cells are precursors of circulating endothelial cells.

"Not only were these cells found in higher levels in [cancer] patients compared to healthy volunteers, but endothelial progenitor cells were found in strikingly higher amounts in patients with metastatic disease," Francoise Farace, director of the department of biology of circulating cells at the Gustave Roussy Cancer Institute, said in a news release from the American Association for Cancer Research.

The finding that children with metastatic cancer had much higher levels of these cells than healthy children was a surprise, the researchers indicated.

"This implies that these endothelial cells most likely play a role in the development of cancer in children," Farace said. "We also observed a large range of cell levels in patients with various tumor types. In some cases, very high levels were observed, which means their role may be very important."

The study appears July 15 in Clinical Cancer Research.

Further research is needed to confirm whether these cells play a role in metastasis. If so, the researchers suggested, testing levels of the cells could improve early detection of metastatic cancer, and the cells could be targeted by new drugs to prevent the spread of cancer.

SOURCE: American Association for Cancer Research, news release, July 15, 2009