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Chlamydia pneumoniae Infection and Risk of Lung Cancer

¹ Department of Epidemiology, University of Washington, Seattle, WA; ² Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA; ³ Center for Health Studies, Group Health Cooperative, Seattle, WA; ⁴ Division of Infectious Diseases, Johns Hopkins University, Baltimore, MD; ⁵ Swedish Cancer Institute, Seattle, WA

Requests for reprints: Alyson J. Littman, Division of Public Health Sciences, Fred Hutchinson Cancer Research Center and Department of Epidemiology, University of Washington, 1100 Fairview Avenue North, M4-B402, P.O. Box 19024, Seattle, WA 98109-1024. Phone: 206-667-7707; Fax: 206-667-4787. E-mail: alittman{at}fhcrc.org

Infection with Chlamydia pneumoniae may be associated with an increased risk of lung cancer. We conducted a matched case-control study (508 pairs) nested within a large prospective study to investigate whether IgA antibody titers to C. pneumoniae measured by the microimmunofluorescence test are associated with lung cancer risk after controlling for confounders. Individuals with antibody titers 16 had 1.2 times the risk of lung cancer (95% confidence interval, 0.9-1.6) compared to those with lower titers. There was a significant trend (P = 0.007) of increasing odds ratios with increasing IgA titers primarily due to an odds ratio of 2.8 (95% confidence interval, 1.1-6.7) associated with titers 256. Lung cancer risk associated with IgA titers 16 was stronger among former smokers. To better understand predictors of IgA seropositivity, we also examined demographic, lifestyle, dietary, and medical correlates of IgA titers 16 among controls. Those with race not classified as White or Black were more likely to have IgA titers 16; there were no significant differences in seropositivity by smoking behaviors. In summary, the adjusted odds ratio for lung cancer associated with IgA titers 16 was compatible with a weakly positive association, although nondifferential measurement error of antibody titers may have resulted in a conservative bias. Future studies using precise measures of chronic C. pneumoniae status are needed to better determine the role of this organism in the etiology of lung cancer.

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