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Epidemiology and Cancer Control |
Department of Human Genetics, University of California Los Angeles School of Medicine, Los Angeles, CA 90095-7088 (Z.F.); Department of Ambulatory Care and Prevention, Harvard Medical School and Harvard Pilgrim Health Care, Boston, MA 02215 (M.K.); Department of Community Medicine and Health Care, University of Connecticut School of Medicine, Farmington, CT 06030-6325 (D.I.G.); USA
2 Address correspondence to Martin Kulldorff, Department of Ambulatory Care and Prevention, Harvard Medical School and Harvard Pilgrim Health Care, 133 Brookline Avenue, 6th Floor, Boston, MA 02215, USA (Martin_Kulldorff{at}hms.harvard.edu).
Abstract
The Atlas of Cancer Mortality in the United States, 1950-94 (Devesa et al.) published in 1999 by the National Institutes of Health suggests that there are elevated rates of brain and other nervous system cancer in the northwestern, north central, and southeastern parts of the country. Being descriptive in nature, the atlas does not evaluate whether observed patterns are simply due to random variation or if they are reflective of true geographical differences in disease risk or treatment practices. To formally test for geographical clustering of disease, we analyzed U.S. brain cancer mortality data from 1986 to 1995 with Tango's Excess Events test, the Cuzick-Edwards k-Nearest-Neighbors test, and the spatial scan statistic. All tests revealed statistically significant geographical clustering for both adult men and women. The spatial scan statistic indicated that the most likely cluster of high mortality was in parts of Arkansas, Mississippi, and Oklahoma (relative risk [RR] = 1.22, P < 0.0001) for women and in parts of Tennessee and Kentucky (RR = 1.15, P < 0.0001) for men. Several secondary clusters were detected, but there were no statistically significant clusters of a very localized nature and a high RR. For childhood brain cancer, there were no statistically significant geographical clusters. It is reassuring that no local brain cancer mortality "hot spots" with very high RRs were found. While the causes of the large geographical clusters with modest RRs are unclear, the geographical pattern of brain cancer mortality provides valuable information that can help in formulating etiological hypotheses and in targeting high-risk populations for further epidemiological and health services research.
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