Ozone, nitrogen dioxide and lung cancer: a review of some recent issues and problems

Lung cancer in man is a common disease. There is some recent concern that oxidant air pollutants might be a contributing risk factor. Experimental data show that ozone and NO2 increase incidence and multiplicity of lung tumors in strain A mice; however, the data are not always statistically significant. Also it depends on experimental design whether ozone enhances or inhibits the development of lung tumors in mice. Similarly, ozone and nitrogen dioxide enhance lung colonization by cancer cells injected intravenously following exposure to the air pollutants, whereas NO2 kills lung metastases if cells are injected prior to exposure. Both ozone and NO2 modulate the proliferation of pulmonary neuroendocrine cells, the precursor cells for small cell lung cancer. It is concluded that there is little evidence to implicate ozone or NO2 directly as pulmonary carcinogens, but that they might modify and influence the carcinogenic process in the lung.