Twenty-two years of cancer cluster investigations at the Centers for Disease Control

Beginning in 1961, the Centers for Disease Control investigated 108 cancer clusters and reported the findings in Epidemic Aid Reports. The clusters studied were of leukemia (38%), leukemia and lymphoma (30%), leukemia and other cancer combinations (13%), and all other cancer or combinations (19%). These clusters occurred in 29 states and five foreign countries, with the largest numbers from Connecticut (11), California (eight), Illinois (eight), New York (eight), Georgia (seven), Pennsylvania (six), and Iowa (five). All other states reported less than five. Eight different data collection methods were used, often in combinations, and four types of laboratory methods on four different specimen types. Although 14 different categories of associations were reported, no clear cause was found for any cluster. Nonetheless, concern about clusters by the public and media, and the need to investigate them, warrants the development of a uniform approach for use by local health departments.