Mediastinal lymph node metastasis model by orthotopic intrapulmonary implantation of Lewis lung carcinoma cells in mice

This study is designed to establish a pulmonary tumour model to investigate the biology and therapy of lung cancer in mice. Current methods for formin g a solitary intrapulmonary nodule and subsequent metastasis to mediastinal lymph nodes are not well defined. Lewis lung carcinoma (LLC) cell suspensi ons were orthotopically introduced into the lung parenchyma of C57/BL6 mice via a limited skin incision without thoracotomy followed by direct punctur e through the intercostal space. The implantation process was performed wit hin approximately 50 s per mouse, and the operative mortality was less than 5%. Single pulmonary nodules developed at the implanted site in 93% of ani mals and subsequent mediastinal lymph node metastasis was observed in all m ice that formed a lung nodule after intrapulmonary implantation. The size o f tumour nodule and the weight of mediastinal lymph node increased in a tim e-dependent manner. The mean survival time of mice implanted successfully w ith LLC cells was 21 +/- 2 days (range 19-24 days). Histopathological analy sis revealed that no metastatic tumour was detectable in the mediastinal ly mph nodes on day 11, but metastatic foci at mediastinal lymph nodes were cl early observed on days 17 and 21 after implantation. Other metastases in di stant organs or lymph nodes were not observed at 21 days after the implanta tion. Comparative studies with intrapleural and intravenous injections of L LC cells suggest that the mediastinal lymph node metastasis by intrapulmona ry impantation is due to the release of tumour cells from the primary nodul e, and not due to extrapulmonary leakage of cells. An intravenous administr ation of cis-diamine dichrolo platinum on day 1 after tumour implantation t ended to suppress the primary tumour nodule and significantly inhibited lym ph node metastasis. Thus, a solitary pulmonary tumour nodule model with lym ph node metastasis approximates clinical lung cancer and may provide a usef ul basis for lung cancer research.