[Biological origins of malignant tumors]

With respect to the recent discoveries related to activation and effects of oncogenes, it should be postulated that malignant transformation is due to their inappropriate activation. The postulate must be taken into account when analyzing any other question concerning malignant tumors, e.g. the role of genetic and environmental factors, defence mechanisms, strategy of prevention and treatment, etc. It is argued in this paper that a) in principle, tumors are caused by the events occurring within the body (oxidative radicals that damage DNA), whereas the environmental factors influence the incidence of certain tumors only superficially, eliciting no effect upon the overall tumor incidence; b) malignant transformation (tumors) is one of the consequences of biological deterioration of the body which, like aging, is caused by mutation accumulation; the death due to a malignant tumor is "one of the mechanisms of dying due to the aging process", c) congenital resistance to tumors mostly concerns the quality of DNA, less the influence of classical defence mechanisms, like immune system; d) malignant tumors are relatively more frequent today, which should not be ascribed to (increased) environmental pollution but is due to the increased longevity of contemporary man, and possibly to negative selection materialized through extremely effective modern medicine. Future research will bring about detailed understanding of the mechanisms of action and interaction of oncogenes in the process of cell malignant transformation for numerous types of tumors, elucidation of the role of oncogenic viruses and, much later, use of drugs providing protection against oncogenic viruses and selectively killing the transformed cells, at least in some (early) phases of the disease.(ABSTRACT TRUNCATED AT 250 WORDS)