Inhalation of NO₂and Blood Borne Cancer Cell Spread to the Lungs

An experimental model was designed where the frequency of blood-borne cancer cell metastases to the lungs of animals was used as an indicator to detect adverse effects of inhaled nitrogen dioxide (NO2). Animals were exposed to air containing 0.40 +/- 0.05 ppm or 0.80 +/- 0.05 ppm of NO2. After the appropriate exposure periods, the animals were infused intravenously with B16 mouse melanoma cells. At 3 wk post-infusion the animals were killed and the lungs were examined for melanoma nodule development. The lungs of the NO2-exposed animals contained a significantly higher number of melanoma nodules than the lungs of control animals (P less than .0025). These results indicate that inhalation of ambient or near ambient levels of NO2 influences the metastasis of blood-borne cancer cells. This raises the possibility that similar events may occur in the human population.