Nitrogen dioxide (NO2) inhalation, formation of microthrombi in lungs and cancer metastasis

It is recognized that cancer cells may be introduced into circulation during surgical removal of a malignant neoplasm. The fate of these cells depends upon many factors. In this paper we present findings from an animal model which indicate that inhalation of nitrogen dioxide facilitates blood-borne cancer cell metastasis to lungs by injuring lung capillary endothelium and formation of microthrombi. Lung capillaries were evaluated by light and electron microscopy. The main lesions observed were microthrombi and injury to capillary endothelial cells, following 6 weeks of 0.35 +/- 0.05 ppm NO2 exposure. The blood-borne cancer cell metastasis was studied utilizing B16 melanoma cells in C57Bl/6J mice. A correlation was observed between increased incidence of microthrombi, endothelial cell injury and lung metastasis in exposed animals. Other adverse NO2 effects such as impairment of immune system may also participate. Inhalation of nitrogen dioxide and other air pollutants may play a significant role in enhancement of metastasis and blood vessel associated disorders.