Sex Hormones and Cancer: Some Effects of the Interplay of Sex Hormones upon the Incidence of Mammary Cancer in Mice

During the last decade many investigators have interested themselves in the study of the hormones of the sex glands and the parts which they play in the physiology of the individual. As often happens when a mass of data is collected by a number of individuals, many divergent and conflicting findings have been published. Out of this mass of data, however, certain principles seem to be generally accepted. Among these is the opinion that the secretions of the various organs do not act independently but are all dependent, one upon the other, and work in a system of checks and balances, any upset in which leads to abnormal physiological function. From the results of the work done with the ovarian hormones and some of the closely allied synthetic hydrocarbons, it appears that these substances, acting upon or accumulating in the mammary tissue of mice, upset the hormonal balance and instigate the formation of neoplasms. In the dilute brown strain of mice, for instance, the hormones of estrus, pregnancy, and lactation stimulate the appearance of adenomas and adenocarcinomas of the breast in 65 to 100 per cent of the breeding females. If, however, females of this strain are kept as virgins, the stimulation of the hormones which produce estrus alone is sufficient to cause the glands to become cancerous in but 50 per cent of the individuals (1). It appears, therefore, that both quantitative and qualitative variations in the carcinogenic stimulants may bring about changes in the incidence of cancer in these animals.