Three older cases from 1990 and 1992 are not officially part of the cluster. They admit that, as with virtually every other cancer cluster studied in the past 40 years, a cause may never be found. From 1961 through 1982, the federal Centers for Disease Control investigated 108 cancer clusters but found no obvious cause for any. The CDC stopped initiating cluster investigations after 1982 and now assists local probes when asked. Thomas Sinks, associate director for science of the CDC's environmental health center, says that in a handful of instances since 1982, preventable causes have been found, but they involved extremely rare cancers or known carcinogens.
Critics say the government's standards of proof are impossibly high.
Va. Federal agencies are afraid of being sued by large corporations or even state and local governments, Gibbs says. The disease causes patients to produce too many immature white blood cells, weakening the body's immune system and hampering the blood's ability to clot and carry oxygen. Nationally, four of five children survive ALL, and there have been no deaths among the Fallon children. If environmental contaminants are causing Fallon's cluster, as many residents here believe, experts also would expect to see AML cases. Many suspect the city's water, but a panel of cancer experts discounted the theory because high levels of naturally occurring arsenic had been present in the groundwater for at least 60 years before the cancers appeared.