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BIOLOGY OF THE LABORATORY MOUSE 



tumor shows a central amorphous mass which grades over into desquamated 

 stratified squamous epithehum. This in turn grades over into definite 

 adenocarcinoma. This can be considered as adeno-acanthoma, but a more 

 probable explanation is that metaplasia has occurred changing glandular 

 epithelial cells into stratified squamous epithelium (Fig. loiA). 



These two characteristics in their most extreme manifestations could be 

 considered as special types of breast cancer. However, an interpretation of 



Fig. loi. — Two features frequently observed in adenocarcinoma of the mammary 

 gland. A, metaplasia of the glandular epithelium in a nest of tumor cells (center of 

 figure) to keratinized squamous epithelium (X200); B, cystic blood-filled spaces sur- 

 rounded by the tumor cells of adenocarcinoma (X200). 



the histological picture presented by the various forms assumed by 

 adenocarcinoma of the mammary gland probably does not require these 

 subdivisions. 



Carcinoma Simplex of the Mammary Glands 



Histologically this tumor is so undifferentiated that its appearance is 

 frequently difficult to associate with that of the mammary gland from which 

 it originated (Fig. 102). However, one can find small foci and traces of 

 adenocarcinoma that blend with the carcinoma simplex cells forming the 

 bulk of the tumor mass. 



The architecture of the tumor shows compact masses of epithelial tumor 

 cells growing in long, broad, branching and anastomosing bands or in a com- 



