© 1999 by Oxford University Press
Journal of the National Cancer Institute, Vol. 91, No. 7, 648-649,
April 7, 1999
© 1999 Oxford University Press
CORRESPONDENCE |
RESPONSES - Re: Trends in Reported Incidence of Primary Malignant Brain Tumors in Children in the United States
Affiliations of author: Department of Radiology, Dartmouth-Hitchcock Medical Center, Lebanon, NH, and Center for the Evaluative Clinical Sciences, Department of Community and Family Medicine, Dartmouth Medical School, Hanover, NH.
Correspondence to: William C. Black, M.D., Department of Radiology, Dartmouth-Hitchcock Medical Center, 1 Medical Center Dr., Lebanon, NH, 03756 (e-mail: William.Black{at}Hitchcock.org).
Dr. Forman believes that I overlooked two critical points in my editorial on the reported incidence of primary malignant tumors in children, the first point being that these tumors are not silent. However, even if this point is completely true and all magnetic resonance imaging (MRI)-detectable brain tumors would produce clinical manifestations within 10 years of detection, the reported incidence should increase with the use of MRI. As I pointed out in my editorial, there are published accounts of cerebral tumors being misdiagnosed as idiopathic epilepsy and brain stem tumors being misdiagnosed as aqueductal stenosis and even asthma. Such misdiagnoses are much less likely to occur in patients who have had a brain MRI, and a decrease in misdiagnosis is probably partially responsible for the reported increase in incidence.
In addition, Dr. Forman's first point is not completely true. As I argued in my editorial, some of the smaller tumors detectable by MRI—particularly the focal low-grade lesions (1) in the brain stem—may remain asymptomatic throughout childhood and possibly even throughout a normal life span. This lack of symptoms should not be surprising. During the past few decades, advances in testing have led to a dramatic increase in the detection throughout the body of tumors that have a histologic appearance of malignancy. In general, "malignant" tumors detected incidentally or by screening are much less aggressive than their symptomatic counterparts (2-5). Although almost all children with a primary malignant brain tumor detected by MRI have some symptoms that prompted the examination, in some cases the symptoms and tumor may be unrelated.
Dr. Forman's second point is that the slight decrease in the mortality from primary malignant tumors in children is evidence for an increase in its incidence. This reasoning, however, is based on the assumption that treatment has become much more effective. While this is possible, it cannot be reliably inferred from historical comparisons of survival, precisely because of the dramatic advances in MRI (6).
Finally, I did not say that we should ignore the reported increase in incidence but rather that we "should not panic or be quick to point blame" at a suspected etiologic agent when the reported increase can be easily explained by increased detection. As I pointed out, a real, coincidental increase in incidence cannot be completely excluded, but neither can a real, coincidental decrease.
REFERENCES
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4 Johansson JE, Holmberg L, Johansson S, Bergstrom R, Adami HO. Fifteen-year survival in prostate cancer. A prospective, population-based study in Sweden [published erratum appears in JAMA 1997;278: 206]. JAMA 1997;277:467-71.[Abstract]cancerlit;97172186
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Yamamoto K, Hanada R, Kikuchi A, Ichikawa M, Aihara T,
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6
Black WC, Welch HG. Advances in diagnostic imaging and
overestimations of disease prevalence and the benefits of therapy. N Engl J Med 1993;328:1237-43.
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