Environmental factors may be linked to the development of leukemia in children in the Fallon area and in Arizona, according to scientists.

Researchers from the University of Nevada, Reno, the University of Arizona, and the University of California, San Francisco, think the first genetic change might have occurred before the children were born or during infancy. A second could have come just before the onset of leukemia.

"What primes the pump?" asked Mark Witten, a toxicologist at the University of Arizona who has been researching the Fallon cluster and a similar outbreak in Sierra Vista, Ariz., since 2002.

"I think we're making some very good progress. The answer may be too late to help Fallon, but it may help prevent future occurrences of leukemia clusters."

The scientists met Monday at UNR to study some of the results of genetic, environmental and water studies into the cancer cluster that sickened 17 children and killed three in Fallon since 1997.

Witten said the clusters in Nevada and Arizona might have been preceded by an outbreak of childhood shingles, a disease usually found in adults exposed to chicken pox as children.

Witten and his partner, Arizona tree-ring scientist Paul Sheppard, have shown in previous studies that both areas have unusually high amounts of tungsten in the environments. The scientists are doing mouse studies to determine how tungsten might cause gene mutations, especially those which have been linked to leukemia.

"Different cancers vary widely in their genetic signatures," said Dr. William Murphy of the University of Nevada School of Medicine. "Fallon may provide a window where maybe we can understand cancer or just leukemia in general."

Joseph Wiemels, a UCSF genetics researcher, said Fallon is the most striking cluster ever studied. He said the theory that the disease is caused by two "hits, at different times, from different causes and with different mechanisms" is the most promising path for research.

"Since this is a rare cluster, it may have a rare cause," Wiemels said.

Chris Pritsos of UNR is examining tungsten, arsenic and the radioactive isotope polonium-210 in Fallon's groundwater to determine if those elements might have some link to the cluster. He is exposing rats to water with various concentrations of those elements to see if the exposure causes genetic damage.

Ralph Seiler of the U.S. Geologic Survey is overseeing the tests of Churchill County well water.

The research was funded by $750,000 in federal grants obtained by U.S. Sen. Harry Reid, D-Nev., and administered by the Environmental Protection Agency and UNR. Witten and Sheppard also have received grants from the Gerber Foundation.

— Associated Press