American Journal of Epidemiology Advance Access originally published online on December 21, 2005
American Journal of Epidemiology 2006 163(4):395-396; doi:10.1093/aje/kwj066
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Letter to the Editor |
TURNER ET AL. REPLY
1 R. Samuel McLaughlin Centre for Population Health Risk Assessment, Institute of Population Health, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5
2 Department of Epidemiology and Community Medicine, Faculty of Medicine, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5
3 Unité de recherche en épidémiologie, Centre de recherche du CHUM, Université de Montréal, Montréal, Québec, Canada H2W 1T7
4 Department of Epidemiology and Surveillance Research, American Cancer Society, Atlanta, GA 30329
e-mail: mturner{at}uottawa.ca
We thank Schabath et al. (1
) for their comments on our recent paper (2). In their letter, they describe the results of recently published epidemiologic studies examining the association between a history of allergy and lung cancer risk (2–4), emphasizing that recent results appear to support an inverse relation. However, these results need to be interpreted with caution.
Our recent analysis of the American Cancer Society cohort does not provide strong evidence for an inverse relation between a history of allergy and lung cancer mortality. Smoking is a vitally important risk factor for lung cancer. Because of a potential, complex interrelationship among allergies, smoking, and lung cancer, a potential allergy–lung cancer relation is best evaluated among never smokers, where the possibility for residual confounding by cigarette smoking is minimized (5). As Schabath et al. (1) point out, we found no association among those persons with a history of hay fever (relative risk (RR) = 1.02, 95 percent confidence interval (CI): 0.86, 1.21) or both asthma and hay fever and lung cancer mortality in never smokers (RR = 0.83, 95 percent CI: 0.56, 1.22) (2).
Schabath et al. (3) also reported no significant association between a history of hay fever and lung cancer among never smokers (odds ratio (OR) = 0.81, 95 percent CI: 0.53, 1.23) in their recent case-control study. Similarly, no association was found for risk of lung cancer among former smokers who had quit smoking at least 20 years ago (RR = 0.96, 95 percent CI: 0.59, 1.54); for them, the possibility for confounding by cigarette smoking may be less in comparison with those who had quit smoking more recently, for whom strong significant inverse associations were observed.
Lastly, the recent case-control study by Castaing et al. (4), which involved only 11 never smokers with eczema, also reported no significant association between a history of eczema and lung cancer risk among never smokers (OR = 0.55, 95 percent CI: 0.28,1.08). Other studies of lung cancer and allergy (not including asthma) were unable to examine risk among never smokers (6–10).
Collectively, the evidence to support an inverse relation between a history of allergy and lung cancer is limited. Previous studies of never smokers have not reported any significant findings, and some may be associated with biases due to hospital-based recruitment and may also be subject to potential confounding by other important environmental and lifestyle factors, including socioeconomic status and occupational exposures. We agree that further research in the area of allergy and cancer is needed in light of evidence of potential inverse associations for other cancer sites (5) as well as a potential positive association reported in a recent meta-analysis between a history of asthma and lung cancer risk (11). At this point, however, the evidence for an inverse association between other indicators of allergic status and lung cancer risk is inconclusive.
ACKNOWLEDGMENTS
Conflict of interest: none declared.
References
- Schabath MB, Gorlova OY, Spitz MR. Re: "Cancer mortality among US men and women with asthma and hay fever." (Letter). Am J Epidemiol (DOI 10.1093/aje/kwj065).
- Turner MC, Chen Y, Krewski D, et al. Cancer mortality among US men and women with asthma and hay fever. Am J Epidemiol 2005;162:212–21.
[Abstract/Free Full Text] - Schabath MB, Delclos GL, Martynowicz MM, et al. Opposing effects of emphysema, hay fever, and select genetic variants on lung cancer risk. Am J Epidemiol 2005;161:412–22.
[Abstract/Free Full Text] - Castaing M, Youngson J, Zaridze D, et al. Is the risk of lung cancer reduced among eczema patients? Am J Epidemiol 2005;162:542–7.
[Abstract/Free Full Text] - Turner MC, Chen Y, Krewski D, et al. An overview of the association between allergy and cancer. Int J Cancer (in press).
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- Talbot-Smith A, Fritschi L, Divitini M, et al. Allergy, atopy, and cancer: a prospective study of the 1981 Busselton Cohort. Am J Epidemiol 2003;157:606–12.
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