The University of Louisville Journal of Respiratory Infections


The author(s) received no specific funding for this work.


Introduction: The degree of association and type of causal versus non-causal relationship between pneumonia and lung cancer (LC) are evolving discussions. We reviewed English publications on the degree of association between pneumonia and subsequent LC.

Methods: We searched the PubMed database using key words for pneumonia, LC, and chlamydia infection. We selected peer-reviewed studies of patients with pneumonia and LC. Case reports and other literature reviews were excluded from this review.

Results: Five studies examined the incidence and/or risk of LC for a total of 415,750 patients, and four studies examined cases with Chlamydia pneumoniae chronic infection at the time of diagnosis of LC for a total of 1,467 patients. The overall risk and/or incidence of LC after pneumonia was from 2.3% to 10% for a median follow-up ranging from 109 days to 4.2 years. Three studies reported current tobacco smoking status, which ranged from 27.7% to 45% among those with LC. A history of prior malignancy was reported in 22.5% of patients with LC. Chlamydia IgA and LC were statistically non-significantly associated regardless of the age of the patients. In one study, Chlamydia HP-60 IgG > 1:50 was associated with significantly increased odds of LC in two respective models (ORs of 1.34 [95% CI 1.06–1.69] and 1.30 [95% CI 1.02–1.67]). A fourth study reported C. pneumoniae IgA > 64 titers to be 58%, 29%, and 5.5% among patients with LC, without LC, and healthy blood donors, respectively.

Conclusions: The incidence of LC was reported to range from 2.3% to 10.3% following an episode of pneumonia. There is limited evidence of the association of chronic Chlamydia infection with LC, and Chlamydia could be a causal cofactor of LC.



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