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BIOLOGY OF THE LABOILiTORY MOUSE 



granules. The cytoplasm is fairly abundant and eosinophilic. These cells 

 vary somewhat in size. Mitoses are fairly frequent. On the surfaces of the 

 papillae and within the gland-hke formations the epithelial cells vary from 

 one to several cell layers in thickness and normal orientation is frequently 

 lost. Invasion of surrounding normal structures and metastases to the 

 lungs occur. 



stroma Cyst Papillae 



Fig. g8. — Papillary cyst adenocarcinoma of the mammary gland (X200). 



The distinguishing characteristics are large and small branching and 

 anastomosing papillary tumor growths within cyst-like cavities which are 

 often so filled with these papillary structures that the cysts are poorly 

 defined. The walls of the cysts are fined by medium sized cuboidal or low 

 columnar epithelial cells which also extend over the surfaces of the branching 

 papillary formations. Here they form a cover of one to several cell layers in 

 thickness. The stroma forms a definite core of connective tissue containing 

 thin-walled blood vessels in the papifiary structures, and the stroma may not 

 be clearly defined in the distal portions of their branches. However, stromal 



