SPONTANEOUS NEOPLASMS IN MICE 189 



They have a small amount of eosinophilic cytoplasm and oval, somewhat 

 hyperchromatic nuclei. 



The lumena of these glands are very prominent. Between the glands the 

 supporting stroma may be reduced to narrow but conspicuous septa of dense 

 fibrous connective tissue containing some thin-walled blood vessels. 



The chief characteristic of this type of tumor is the enormous, irregularly 

 branching, duct-like structures whose lumena may extend for considerable 

 distances. The walls, which are composed of compact tumor cells, are from 

 four or five to twenty or more cells in thickness and follow fairly closely the 

 contours of the lumena. This gives the appearance of giant thick-walled 

 ducts. Invasion of adjacent normal tissue is commonly seen and metastases 

 in the lungs are often found. 



In quite a number of breast tumors there can be seen large and small, 

 blood-filled, cyst-like spaces which are often clustered closely together. 

 These are always surrounded by small epithelial tumor cells, which may form 

 compact strands varying from three or four to many cell layers in thickness. 

 These cells may or may not show some flattening where they come in close 

 contact with the blood-filled cyst-like spaces. These spaces have an acellu- 

 lar, membrane-like, eosinophilic zone between the epithelial cells and the 

 blood. In some instances there are scattered, flattened cells present which 

 suggest an endothelial lining within these spaces. 



Some investigators have considered these cystic tumors as belonging to a 

 type called hemorrhagic cyst adenocarcinoma (Fig. loiB). One can find 

 simple adenocarcinoma with foci where clusters of blood filled spaces are 

 separated by thin, compressed strands of epithelial tumor cells. Similar 

 spaces are also frequently found in cases of adenocarcinoma, variable type, as 

 well as in nests of tumor cells which are in the midst of and continuous with 

 intracanalicular adenocarcinoma and even papillary cyst adenocarcinoma. 

 In the latter type papillary growths may extend into the cyst-like blood 

 filled spaces. When this is taken into consideration, it may be advisable to 

 consider these hemorrhagic cysts not as a separate type but more as a com- 

 mon characteristic of adenocarcinomas in general. 



In gross observation these tumors show many bulging, blood filled cysts. 

 The tumor is turgid and when cut open will collapse into a soft hemorrhagic 

 mass. 



There is a somewhat similar situation in the case of the frequent appear- 

 ance of epithelial pearls, composed of cornified, squamous epithelial cells 

 grouped in concentrically arranged foci (23). These pearls can be found in 

 all types of adenocarcinoma. This may even progress to the stage where the 



