The Mechanism of Hormonal Carcinogenesis

Abstract

The study of the induction of tumors by hormones can serve as a useful approach to learning more about the mechanism of carcinogenesis. A survey of what is known at this time about hormones as carcinogenic factors reveals that the hormones which have been assumed to have a carcinogenic effect have 1 property in common i.e. they are all growth-stimulating hormones acting on particular target organs. This group of hormones includes the trophic hormones of the hypophysis and the steroid hormones. Growth hormone or somatotrophic hormone has no special target organ; it is a metabolic hormone which exerts its influence by means of a series of interventions in the intermediary metabolism. The relation between growth-stimulating effect and carcinogenic effect is obvious in the primary endocrine organs and the secondary sex organs but this relation seems questionable in other organs and in the lymphoid tissue. The action of estrogenic hormone as a leukemogenic agent is still unexplained as is the mechanism of the carcinogenic effect of hormones in the genesis of liver and bone tumors. If there is in the primary endocrine organs and the secondary sex organs a relationship between growth stimulation and carcinogenic effect then the carcinogenic effect of a hormone must be expected in the target organ of this particular hormone. Generally it may be stated that the carcinogenic effect of a hormone is related to the amount of the hormone acting on its target organ. The induction of ovarian tumors is caused by the uninhibited production and release of gonadotropin hormones by the hypophysis. Estrogenic hormones inhibit this production or secretion. Experiments are reported that show that continuous treatment with hormones is much more effective in the induction of cancer than discontinuous treatment. In the genesis of spontaneous tumors the supernormal effect of a hormone may be caused by an increased amount of the hormone acting on the target organ as the consequence of an increased production or secretion. There is also the possibility of another type of hormonal imbalance i.e. affecting not the carcinogenic hormone-producing organs but the target organs. A discussion is included.