Cigarette smoking and the risk of pulmonary metastasis from breast cancer.

STUDY OBJECTIVES To determine whether there is an association between cigarette smoking and the development of pulmonary metastatic disease among women with breast cancer. DESIGN A case-control study. SETTING The University of California, Davis Medical Center. PARTICIPANTS Eighty-seven women patients with unilateral, invasive breast cancer and pulmonary metastatic disease were identified as cases, and each patient was matched with two control patients who did not have pulmonary metastatic disease. Case patients and control patients were matched for year of diagnosis, age at diagnosis, size of primary tumor, and nodal status. DATA ANALYSIS Multivariate analysis using conditional logistic regression was used to determine the odds of smoking among women with pulmonary metastatic disease compared to matched control patients without pulmonary metastatic disease, after correction for potential confounding factors. RESULTS Thirty-eight percent of the case patients vs 29% of the control patients were classified as ever-smokers; 24.1% of case patients were actively smoking at the time of breast cancer diagnosis vs 15.3% of the control patients. The unadjusted odds ratio for active smoking was 1.76 for women with pulmonary metastatic disease compared to women without pulmonary metastatic disease (p = 0.06). In the final multivariate model, the odds ratio for active smoking among women with pulmonary metastatic disease was 1.96 (p = 0.06). CONCLUSIONS There appears to be an association between cigarette smoking and the development of pulmonary metastatic disease among women with breast cancer. This may explain the previously noted higher breast cancer fatality rate among smokers. The relationship between smoking behavior and pulmonary metastasis from breast and other cancers warrants further investigation.