Background: Whereas extensive research has explored the effect of environmental factors on the etiology of specific cancers, the influence of exposures such as smoking on risk of site-specific metastasis is unknown. We investigated the association of cigarette smoking with lung metastasis in esophageal cancer. Methods: We conducted a case-control study of esophageal cancer patients from two centers, comparing cases with lung metastases to controls without lung metastases. Information was gathered from medical records on smoking history, imaging results, site(s) of metastasis, and other patient and tumor characteristics. We used logistic regression to assess association. Results: We identified 354 esophageal cancer cases; smoking status was known in 289 (82%). Among patients with lung metastases, 73.6% (39 of 53) were ever smokers, versus 47.8% (144 of 301) of patients without lung metastases [P = 0.001; summary odds ratio (OR), 2.52; 95% confidence interval (95% CI), 1.17-5.45; stratified by histology]. Smoking was associated with a nonsignificant increased adjusted odds of lung metastasis (OR, 1.89; 95% CI, 0.804.46). Upper esophageal subsite (OR, 4.71; 95% CI, 1.20-18.5), but not histology (squamous OR 0.65,95% CI 0.27-1.60), was associated with lung metastasis. Compared with the combined never/unknown smoking status group, smoking was associated with a significantly increased odds of lung metastasis (OR, 2.35; 95% CI, 1.11-4.97). There was no association between liver metastasis and smoking (OR, 0.88; 95% CI, 0.42-1.83). Conclusions: Smoking is associated with increased odds of lung metastasis from esophageal cancer, and this relationship seems to be site specific. Future studies are needed to determine whether smoking affects the tumor cell or the site of metastasis, and whether this changes the survival outcome.
