The necessity is substantiated to discriminate between the two notions: the oncogenic potency of cell genome and the conditions which either favour or prevent its realization. Both epigenetic alterations and mutations may cause neoplastic transformation of the cell but the expression of the tumor phenotype, composed of normal structural and functional elements, occurs exclusively at the epigenetic level. An impaired selectivity of nucleus-to-cytoplasm transport of mRNAs presumably is involved in this process.