Ozone, Nitrogen Dioxide and Lung Cancer

A Review of Some Recent Issues and Problems

Abstract

Cancer of the stomach shows a characteristically high proportion in Japan. However, recently age ad justed death rate of lung cancer shows a marked increasing tendency. It is predicted that the death rate of lung cancer in man will become to the first ranking in 1990. The main causes of lung cancer are concerned to be cigarette smoking and some kind of foods. But, there is some recent concern that oxidant air pollutants such as O₃ and NO₂ also might be a contributing risk factor from some epidemiological data.
Here, we would like to discuss about the experimental data on effects of O₃ and NO₂ on lung tumor formation. These data show that O₃ and NO₂ increase incidence and multiplicity of lung tumors in 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 in jected intravenously following exposure to the air pollutants, whereas NO₂ kills lung metastases if cells are in jected prior to exposure. Both ozone and NO₂modulate 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.