Interpreting Epidemiologic Research and Childhood Leukemia
Sue Rabbitt RoffFaculty of Medicine, Dentistry, and Nursing; Centre for Medical Education; University of Dundee; Dundee DD2 1LR, Scotland
To the Editor.—
In "Interpreting Epidemiologic Research: Lessons From Studies of Childhood Cancer," Linet et al1 rely heavily on the work of Kinlen in suggesting that there is an infectious cause for childhood leukemia related to population movements and increased social contacts. However, a review of Kinlen’s work shows a remarkable shift of his thinking away from the infectious hypotheses. In the late 1980s, Kinlen proposed a comparison between human population crowding as occurred in the creation of the postwar New Towns in the United Kingdom2 and the transmission of feline leukemia among cats living in crowded conditions. In 1990, Kinlen et al3 suggested a child-child transmission among the families in the New Towns. However, in 1991, Kinlen et al4 moved to an adult-child transmission hypothesis, suggesting that an explanation of excesses in childhood leukemia among <5-year-olds near nuclear power stations in west Berkshire in England might be correlated with increased commuting by adults. Kinlen and Hudson5 then looked at the incidence of childhood leukemia (and poliomyelitis) in relation to military encampments in England and Wales in the period of national military service from 1950 to 1963 and reported an excess of leukemia in children <2 years old in the districts with the highest proportion of "incoming" servicemen. From this they concluded that the fact that "the excess of leukemia was greatest in children under 1 year suggests transmission of infection among adults and thence the fetus." However, they did not explore the possibility of preconceptual or in utero etiologies, much less potential exposure related to the application of industrial radiography to armaments manufacture and monitoring that had begun well before the first world war.6 By 1993, Kinlen et al7 hypothesized that the North Sea oil industry might account for paternally mediated increased incidences of childhood leukemia in rural areas in Scotland: "Few children live close to these work sites (and, obviously, none offshore), but the regular home visits of these workers might occasion indirect exposure of their home communities to any effects of the mixing in those unusual work sites." By "oil industry workers" was meant those men working on the construction of the oil terminals and offshore oil rig workers, all of whom potentially would have been in the vicinity of radiation exposures from the widespread use of industrial radiography for monitoring materials used in all aspects of the oil industry. Again the excess occurred mainly in the <5-year-old children. Kinlen and his colleagues noted that the Dounreay-Thurso population, which they had previously thought of solely in terms of the nuclear reprocessing plants, also contained a large number of these oil industry workers as well as those involved in the construction and operation of the nuclear plants.
The next study by Kinlen et al,8 which focused on "nonnuclear construction projects in rural areas" of the United Kingdom, found a 37% excess of leukemia, again in the <5-year-olds, during the period of construction and the following calendar year (ie, the period when preconceptual paternal irradiation might have occurred from exposures to industrial radiography widely used in major construction projects that included power stations, hydroelectric schemes, and oil refineries). It was noted that only 1 plant in the study (Drax) had had a prolonged period of construction work after its operational start, and it alone has shown an excess of childhood leukemia and non-Hodgkin’s lymphoma over an extended period. In 2001, Kinlen and Bramald9 found again that the "effect" seemed to concentrate in the <5-year-olds and was probably confined to the rural areas of Scotland, where the construction industry "may be relatively unusual in often involving work away from home on large projects." The rather forced methodology, with its assumptions about the volume of "paternal occupational contact" in occupations as diverse as school teaching and construction, was applied10 to Swedish data, and it was concluded that, although there was a similar effect among <5-year-olds in very isolated areas, "population mixing (as occurred in Scotland as a result of the North Sea oil industry) is not a necessary requirement for the effect, since comparable mixing has not been a feature of rural Sweden."
Kinlen raised his hypothesis of an infective etiology for childhood leukemia in opposition to the hypothesis of Gardner et al11–14 of preconceptual paternal irradiation as the cause of accepted excesses of the disease in the offspring of radiation workers. As Kinlen has sought to refine his hypothesis, he has never been able to suggest a biological mechanism for the infective process–unlike the advances made in the past decade in understanding the etiology of radiogenic transmission. Yet Kinlen himself has come to the position that the process is one of paternal transmission and occurs frequently among workers in construction industries and offshore oil workers in Scotland. Can it be that Kinlen has evidenced Gardner’s hypothesis, given the role of industrial radiography in these industries?
REFERENCES
- Linet MS, Wacholder S, Zahm SH. Interpreting Epidemiologic Research: Lessons From Studies of Childhood Cancer.
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[Free Full Text] - Kinlen LJ. The relevance of population mixing to the aetiology of childhood leukaemia. In: Crosbie WA, Gittus JH, eds. Medical Response to Effects of Ionising Radiation. London, United Kingdom: Elsevier Applied Science; 1989:272–278
- Kinlen LJ, Clarke K, Hudson C. Evidence from population mixing in British New Towns 1946–85 of an infective basis for childhood leukaemia. Lancet.336 :577 –582
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[Abstract/Free Full Text] - Kinlen LJ, Bramald S. Paternal occupational contact level and childhood leukaemia in rural Scotland: a case-control study. Br J Cancer.2001; 84 :1002 –1007[CrossRef][Web of Science][Medline]
- Kinlen L, Jiang J, Hemminki K. A case-control study of childhood leukaemia and paternal occupational contact level in rural Sweden. Br J Cancer.2002; 86 :732 –737[CrossRef][Web of Science][Medline]
- Gardner MJ, Snee MP, Hall AJ, Powell CA, Downes S, Terrell JD. Results of case-control study of leukaemia and lymphoma among young people near Sellafield plant in West Cumbria. BMJ.1990; 300 :423 –429
- Gardner MJ, Hall AJ, Snee MP, Downes S, Powell PA, Terrell JD. Methods and basic data of case-control study of leukaemia and lymphoma among young people near Sellafield nuclear power plant in West Cumbria. BMJ.1990; 300 :429 –434
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PEDIATRICS (ISSN 1098-4275). ©2004 by the American Academy of Pediatrics
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  L. J. Kinlen Childhood Leukemia and Population Mixing Pediatrics, July 1, 2004; 114(1): 330 - 331. [Full Text] [PDF]
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