OBJECTIVETo set up animal models of the lung cancer induced by Yunnan tin mineral dusts (no radon) in F344 rats and to explore the process of carcinogenesis and pathologic alterations in various stages of malignant transformation in the animal models.

METHODSOne hundred and ninety F344 rats were randomly divided into Yunnan tin mineral dust group (100 rats), furfural physiological saline group (30 rats), physiological saline group (30 rats) and normal control group (30 rats). The intratracheal instillation with mass fraction of 6% suspension liquid mixture Yunnan tin mineral dusts, volume fraction of 2% furfural physiological saline and physiological saline 0.2 ml was performed in the rates once per week respectively except normal control group. Then the rats were sacrificed in batch periodically after one week. The last rat was exposed to the tin mine dusts for 100 weeks. The morphological process and tumor formation were dynamically observed under LM and TEM. Immunohistochemistry detection of cytokeratin of High MW and low MW was used for tumor classification. Pollak stein was used to evaluate the development of fibrosis of lung in the rats.

RESULTSBronchoalveolar inflammation occurred in the early stage after the intratracheal instillation of Yunnan tin mineral dust was performed in F344 rates. Along with reduction of inflammation, collagen fibrils increased at alveolar interstices. Simple hyperplasia, papillary hyperplasia and metaplasia of the epithelial cells in alveolar and bronchi were observed, followed by atypical adenomatous hyperplasia and squamous dysplasia. Lung cancer was induced in the end. Among the 14 cases of lung cancer, 9 cases were adenocarcinoma, 2 squamous cell carcinoma and 3 mixed carcinoma. No lung cancer occurred in other three control groups. There was a significant difference in the malignancy rate between the experimental group and the three control groups (P < 0.01). The squamous metaplasia and squamous carcinoma were found in alveoli that expressed cytokeratin of High MW. Lung fibrosis was found in 31 cases of in the tin mineral dust group. The greater the mineral dust deposit was, the more serious the alveolar fibrosis was.

CONCLUSIONYunnan tin mineral dusts without radon induce lung cancer in rates. The adenocarcinoma and squamous carcinomas induced in F344 rat lung can occur in the alveoli. The further study on whether type II alveolar epithelial cells are the origin cells of adenocarcinoma and some peripheral squamous lung carcinomas is worthwhile.