Breast cancer risk factor

Cigarette smoking appears to be associated with an increased risk of pulmonary metastases in women with breast cancer. The evidence comes from a report by Murin and Inciardi, (1) who studied 87 women with unilateral invasive breast cancer and pulmonary metastatic disease.

Each patient was matched with 2 controls who did not have pulmonary metastatic disease. Patients and controls were matched for year of diagnosis, age at diagnosis, size of primary tumor, and nodal status.

A history of smoking was identified in 38% of patients and 29% of controls; 24.1% of the patients and 15.3% of the controls were actively smoking at the time of breast cancer diagnosis. The odds ratio for active smoking among women with pulmonary metastatic disease was 1.96 (P = .06).

The authors acknowledge that their study did not control for lifestyle factors, such as diet and exercise, that may confound the relationship between smoking and metastatic disease.

In an accompanying editorial, Lillington and Sachs (2) note that while the association between smoking and pulmonary metastases from breast cancer seems logical, it does need to be confirmed by further studies. Possible mechanisms include:

* Inhaled carcinogens from tobacco smoke may be absorbed into the pulmonary circulation, then carried to the site of the primary breast tumor to stimulate the release of tumor material into the systemic veins or lymphatics.

* The effect of the circulating carcinogens from tobacco smoke may stimulate the growth of occult metastases in the lungs.

* Inhaled carcinogens may somehow make the pulmonary tissues more receptive to tumor embolization or lymphangitic spread.

Lillington and Sachs note that the above-mentioned findings underscore the importance of effective smoking cessation interventions for women who are smoking at the time of breast cancer diagnosis. They also emphasize the need for close monitoring of smoking status among women who have stopped smoking in the previous year, since these women clearly are at increased risk for relapse.

(1.) Murin S, Inciardi J. Cigarette smoking and the risk of pulmonary metastasis from breast cancer. Chest. 2001;119:1635-1640.

(2.) Lillington GA, Sachs, DP, Cigarette smoking, pulmonary metastases, and breast carcinoma: coincidence or causality? Chest. 2001;119:1627-1628.