RESUMEN
This report provides evidence for spontaneous transfer of human tumor DNA in vivo to mouse cells by a human small cell lung cancer implanted in nude mice. The transformation of the mouse cells was characterized by the presence of neurosecretory granules, which are hallmarks of small cell lung cancer. The carcinogenicity of the human xenografted tumor DNA was confirmed by transfecting NIH3T3 cells in vitro, suggesting that the human tumor DNA may have been the cause of the transformation of the mouse cells in vivo. The spontaneous induction of malignancy in mouse cells in vivo by human tumor DNA may be a factor of potential importance in tumor cell heterogeneity and propagation of the malignant state for some tumors. The observations support the thesis that some human cancer cells can transform normal cells to become malignant in vivo.