Factors concerned in the chemical induction of mammary cancer.

Attention in this discussion of the factors concerned in the chemical induction of mammary cancer is directed to the following: chemical carcinogens; hormonal mechanisms in carcinogenesis by 20-methylcholanthrene; hormonal mechanisms in carcinogenesis by 2-acetamidofluorene; genetic influences on the composition of the ovarian secretion and its relation to mammary carcinogenesis; time of appearance of breast cancers in mice treated with different carcinogens; two-stage mechanism of chemical mammary carcinogenesis; the effect of lactation; hormone-mimetic properties of carcinogens (estrogen-mimetic activity progresterone-mimetic activity and androgen-mimetic activity); the mechanism of action of chemical carcinogens on the breast; the effect of breast carcinogens on certain other tissues (the ovary the uterus); and the relation of experimental observations in animals to the etiology and treatment of human breast cancer (causative agents hormonal requirements for cancer induction in the human breast occurrence of tumors in more than 1 tissue and stages of carcinogenesis). The evidence for the hormonal activity of some breast carcinogens is fragmentary. It needs to be remembered that little experimental work has been devoted to the demonstration of such hormonal activity. The breast carcinogens which have hormone-mimetic activity are obviously not equivalent to the naturally occurring substances in their physiological action. Experimental evidence exists that the mechanism of carcinogenesis in the breast is a process which occurs by complementary stages. The final clinical manifestation of cancer is only the 1st macroscopic evidence of the process and conversely the initiating agent i.e. the carcinogen is probably not very important once the carcinomatous change has been initiated. There is ample evidence experimentally that hormonal stimulation has an important role in the transformation of affected cells into actively growing tumors. There is also clinical and some experimental evidence that progression of breast cancer occurs from a relatively dependent growth to one which is totally autonomous.