[Induction of the differentiation of tumor cells as an approach to tumor therapy].

Recently, it has been shown clearly that various tumor cells can be induced by differentiation inducers including biological response modifiers, synthetic chemicals and conventional anticancer drugs to differentiate terminally both in vitro and in vivo into cells with normal characteristics. On differentiation, the cells cease to proliferate and lose their transplantability in either nude mice or syngeneic animals. Furthermore, prolongation by the differentiation inducers of survival times of animals inoculated with various tumors was confirmed. These findings suggest that induction of terminal cell differentiation by differentiation inducers is another approach to tumor therapy, that is "differentiation therapy" of tumors. In this review, recent results of basic and clinical studies on the differentiation therapy of tumors are described. The problems and perspectives of differentiation therapy are also discussed.