Leukemia, Radiation, and Hyperthyroidism

  • E. B. Lewis


Saenger et al. (Letters, 19 Mar.) argue that hyperthyroidism per se is responsible for the statistically significant increase in leukemia death rate which they observed in a combined group of 18,379 radioiodine-treated (RAI) and 10,731 surgery-treated (SUR) hyperthyroid patients (1 ). For the years 1946 to 1964 this increase amounted to 1.5 times the expected death rate calculated on the basis of the experience of the U.S. general population. I have examined the origins of this increase by comparing observed numbers of leukemia deaths in each patient group with the corresponding expected numbers calculated on the basis of U.S. age-, sex-, year-specific leukemia death rates (2). The results show that the excessive leukemia death rate is largely confined (i) to patients who were over 50 years of age at the time of treatment; (ii) to patients with the acute rather than the chronic form of the disease; and (iii) to the RAI rather than the SUR group. Moreover, in RAI patients there is a statistically significant excess of acute leukemia deaths (2) occurring between ages 50 and 79 (namely, 9 observed versus 3.6 expected; P = .01); whereas, in SUR patients, although there is an excess of such deaths between ages 50 and 79 (4 observed versus 2.5 expected), the excess is not statistically significant (3).


Acute Leukemia Chronic Form Significant Excess Hyperthyroid Patient Expect Death Rate 
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  1. 1.
    E. L. Saenger, G. E. Thoma, E. A. Tompkins, J. Amer. Med. Assoc. 205, 855 (1968).Google Scholar
  2. 2.
    Based in part on unpublished data on the age-composition of each group supplied by Saenger et al. and unpublished tabulations of acute leukemia deaths (under rubric 204.3) in the United States supplied by the National Center for Health Statistics.Google Scholar
  3. 3.
    Saenger et al. (1) only attempted a comparison of the leukemia experience of the RAI group with that of the SUR group after adjusting for age by the so-called direct method. This method lacks the power to detect even large differences between the two groups, since the number of deaths from acute leukemia, especially in the SUR group, is too small to calculate meaningful age-and sex-specific rates.Google Scholar
  4. 4.
    R. Doll, Br. J. Radiol. 35, 31 (1962).Google Scholar
  5. 5.
    A. Stewart and G. W. Kneale, Lancet 1970-I, 1185 (1970); B. MacMahon, J. Nat. Cancer Inst. 28, 1173 (1962).Google Scholar

Copyright information

© Springer Science+Business Media New York 2004

Authors and Affiliations

  • E. B. Lewis
    • 1
  1. 1.Division of BiologyCalifornia Institute of TechnologyPasadenaUSA

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