56-8 APPENDIX 



The tumor-forming ability of hyperplastic alveolar nodules (and of normal 

 tissues) in a variety of hormonal milieux has been studied, and the results of endocrine 

 manipulations both favoring and opposing tumorous transformation have been re- 

 corded. 932, 933 



Individual nodules with different morphologic or physiologic characteristics 

 are being studied by transplantation into the fat pad, to determine their tumor- 

 forming abilities. For example, lactating and nonlactating nodules from the same 

 donor mouse can be transplanted contralateral^ into a single host (Bern and Nandi, 

 unpublished data). From studies such as these, it should be possible to decide whether 

 greater hormonal sensitivity of nodules — as judged in various ways — is correlated with 

 greater tumor-forming ability. 



By serial transplantation of outgrowths from hyperplastic alveolar nodules, we have 

 revealed the nonhomogeneity of cellular populations comprising individual nodules, 252 

 and we are currently searching for correlations between the tumor potential of various 

 serially transplanted outgrowths and their morphologic (including cytologic) and physio- 

 logic characteristics. The outgrowth sublines that have been maintained have proved 

 to be stable to a considerable degree in regard to the several properties studied. 



Since tissue can be transplanted into the cleared fat pad at any age of the host, 

 the procedure is being utilized in a study of the effect of aging upon normal and neo- 

 plastic mammary growth. Tissues that are transplanted in this fashion are potentially 

 immortal. Such tissues can be transplanted constantly into old mice or into young 

 mice. The effect of age of the host as distinguished from the age of the tissue can be 

 determined, and the use of this method of transplantation in gerontologic studies 

 seems especially promising. 253, 254 



Mammary tissues that have been subjected to various conditions in organ culture 

 can be transplanted back into cleared fat pads and their organ-forming ability de- 

 termined (Faulkin, Rivera, and DeOme, unpublished data). It seems probable that 

 cultures of cells may also lend themselves to this kind of study. 



The differentiation' of embryonic mammary gland may be followed in fat-pad 

 transplants, and some success has already been attained in this type of endeavor 

 (Moretti and Blair, unpublished data). 



Transplantation of tissues of parental strains into hybrid mice has also proved 

 successful in our hands and in those of C. W. Bardin at Baylor University (personal 

 communication) . Normal mammary tissues appear to retain the hormonal responsive- 

 ness characteristic of their source, and this establishes further that such strain-specific 

 responses are determined genetically at the tissue level (Nandi, unpublished data) . 



The possibility of transplantation of tissue into the fat pad is not limited to mammary 

 tissues by any means. We have done very little to date with further utilization of 

 this technique, but it is apparent that some embryonic tissues will survive to an important 

 extent in this new environment (Blair and Moretti, unpublished data) . 



The use of the gland-free mammary fat pad as a site for tissue transplantation may 

 prove to be an excellent tool not only for general investigation of the factors governing 



