Emphysema detected on computed tomography and risk of lung cancer: a systematic review and meta-analysis.

BACKGROUND: Studies exploring the association between emphysema detected on chest computed tomography (CT) and lung cancer have yielded mixed results. Our objective was to systematically review the evidence for this association. METHODS: We searched MEDLINE, EMBASE and the Cochrane Library for the terms "lung cancer", "emphysema" and "computed tomography" without language restriction. Bibliographies were also reviewed and authors contacted for additional information. Human studies in which CTs were performed and assessed for emphysema and in which subjects were evaluated systematically for lung cancer were included. Qualitative synthesis of evidence was performed followed by pooling of effect estimates using a random-effects model. RESULTS: Of 187 citations, 7 were included in the qualitative synthesis and 5 in the meta-analysis. Three studies assessing emphysema visually observed an association with lung cancer, independent of smoking history and airflow obstruction. Three studies using densitometry to detect emphysema found no association with lung cancer. Another study directly comparing automated and visual emphysema detection techniques found only the latter to associate with lung cancer. Among 7368 subjects included in the meta-analysis, 2809 had emphysema on CT and 870 were diagnosed with lung cancer. The pooled adjusted odds ratio for lung cancer in the presence of emphysema on CT was 2.11 (95% CI 1.10-4.04); stratification by detection method yielded OR of 3.50 (95% CI 2.71-4.51) with visually detected emphysema and 1.16 (95% CI 0.48-2.81) with densitometric emphysema. CONCLUSION: Systematic literature review shows emphysema detected visually on CT to be independently associated with increased odds of lung cancer. This association did not hold with automated emphysema detection.