WEST PALM BEACH — When children were coming down with leukemia roughly once a month in a small farming community in western Nevada, health experts were confident they would pinpoint the cause.
Potential culprits weren't hard to find in Fallon, 30 miles from an old underground nuclear test site and not far from a naval air station. Amid one of the largest cancer-cluster investigations in U.S. history, scientists and residents alike said they suspected some type of pollution.
"It's not random," Floyd Sands, whose daughter had leukemia, told the Reno Gazette-Journal in 2001, a year into the seven-year study. "The cause is out there, somewhere in Fallon."
But in the end, the study found no answers. And since 2004, only one new case of childhood leukemia has been reported in Fallon or the surrounding county.
A similar ending without closure may be in store for the Acreage, where more than a year of state investigations has failed to explain a spike of tumors in children's brains and central nervous systems.
In some ways, the Acreage's case is unique among Florida cancer studies: The Palm Beach County community is the only place where the Health Department has ever declared that a suspected cancer cluster exists.
Yet here, too, tests of soil and water have turned up no signs of pollution that could explain the cluster, the state's health and environmental agencies say. Last month, the state Department of Environmental Protection declared that "residential property in the Acreage is safe."
It may be baffling, but it should be no surprise. Rarely, if ever, have scientists found a firm environmental cause for a cancer cluster afflicting a geographic region.
"There's this intuitive sense that seems so straightforward: If there's too much of something occurring, there must be some reason to it," said David Savitz, director of Mount Sinai School of Medicine's Disease Prevention and Public Health Institute in New York. "The problem is, in practice, it just doesn't work that way."
One reason is that cancer is complicated: It has many origins, including random genetic mutations, and not everyone exposed to even high doses of carcinogens will get the disease.
Moreover, scientists say that even if disease rates are normal, some areas are bound to have more cases than others.
Some scientists even argue that chance is the most plausible explanation for a cluster when artificial boundaries are drawn around an area where cases exist. That's how the state determined the cluster boundaries for the Acreage, where health officials say the community experienced four cases of pediatric brain tumors from 2005 to 2007 — when one or two would be normal.
People report about 1,000 potential clusters to state health departments each year, the American Cancer Society says. Only 50 to 150 turn out to be clusters.