[Molecular mechanism of carcinogenesis]

Biological characteristics of cancer cells are thought to be immortalization, transformation (abnormal cell growth) and capacity for tumor invasion and metastasis. Recent studies have revealed that many cellular genes (oncogenes and anti-oncogenes) were activated or suppressed at the level of DNA in cancer cells, and in normal condition the products of these genes have important roles in signal transduction for cell growth as a positive or negative way. Point mutation and unphysiological DNA recombination are considered to be major molecular mechanisms in the alteration of these cellular genes. Further, several genes were found to be involved in invasion and metastasis. However, still a significant portion of cancers remains to be elucidated in terms of unknown cellular (or viral) genes involved in multi-step carcinogenesis. Therefore, we need to continue the basic research on cancer and to initiate the studies on new chemicals, hormones or others by which we could control the activities of known oncogene and anti-oncogene products.