Breast Cancer in Mice as Influenced by Nursing<xref ref-type="fn" rid="fn1"><sup>1</sup></xref><xref ref-type="fn" rid="fn2"><sup>2</sup></xref>

Abstract

Evidence suggests that maternal/extrachromosomal influence may be a factor in mammary carcinogenesis in mice. There are 3 possible methods of transmission to the progeny: 1) by means of the cytoplasm or cytoplasmic inheritance 2) during intrauterine development and 3) by way of the mothers milk while nursing. Various experiments in breast cancer etiology in mice have assumed a correlation between milk/hormonal/susceptibility factors and cancer development. For stock A high-breast tumor breeding females this would suggest development of spontaneous mammary cancer in every female. However this had not been the case. If noncancerous animals of this stock are mated and their progeny continued the incidence of breast tumors among the offspring is very similar to that of the control stock suggesting that these mice are genetically cancerous and would probably develop the condition if they live longer. Other experiments show that breast tumors can occur in a small percentage of animals where none were to be expected suggesting that there may be other contributing factors of unknown origin and/or there may be physiological upsets in the equilibrium or relationship of the known factors and changes characteristic of somatic mutation. Experimental evidence also suggests that an excessive dose of estrogenic hormone may produce carcinoma more easily in males of a strain not susceptible to breast cancer but having the milk factor active than in males of a susceptible strain having the milk factor that is not active.