Abstract
Studies have been carried out to determine whether the inhalation of ambient levels of nitrogen dioxide (NO2), a common air pollutant, could influence the frequency of blood-borne cancer cell metastasis to the lungs. B16 mouse melanoma cells were used as an in vivo test model. the results have indicated that animals inhaling ambient levels of NO2 developed a significantly higher number of melanoma nodules in their lungs than the animals inhaling filtered air. Thus, a new concept for the action of air pollutants is proposed. The question is raised whether similar events are taking place in urban human populations.