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The development of a transfection technique which is based on the transfer of foreign genetic material into permissive cells allows one to isolate and identify the transformed genes in tumors of different etiology [1]. The results which have been obtained in the last few years lead to the conclusion that primary effects in human tumors during their progression are connected with the activation of different genetic elements, among which oncogenes may play an important role [2]. The main aim of this work is the elaboration of an experimental model for the analysis of human tumors and human genome DNA fragments which participate in the process of malignant cell transformation.

The expression of 9 oncogenes in primary tumors and in human tumors passaged in nude mice was tested: a total of 28 tumor types was analyzed. Oncogenes src, fps, and mos were not expressed in any of the tumors tested but oncogene myc was transcribed in most of the tumors and myc was over-expressed in 3 tumors passaged in nude mice (Ewing sarcoma, large intestine carcinoma and kidney carcinoma) and in primary fibrous histiocytoma. Enhanced transcription of ras and fos genes was observed nonspecifically in different tumors. Oncogene sis was activated specifically in metastases of different tumors in lymph nodes.