SPONTANEOUS NEOPLASMS IN MICE 



191 



pact mass without any definite arrangement and with rather inconspicuous 

 stroma. In the first type there is often considerable debris resembHng 

 necrotic material between the bands of tumor cells, and pseudoglandular 

 arrangement around this debris and surrounding the thin-walled blood 

 vessels is not uncommon. Clusters of large and small, blood filled, cystic 

 spaces similar to those observed in adenocarcinoma are sometimes found in 

 this type of tumor. 



The epithelial tumor cells are usually quite large and vary in size. They 

 are compact 1\- arranged with rather indistinct cell boundaries. In outline 





Tumor cell 



■Mitotic figure 





-Normal duct 



^9 -' 







<ir- 



-i<u 



■i' 



-Stroma 



'X:- 



»L 





Fig. 102. — Carcinoma simplex of the mammary gland (X400). 



the cells vary from rounded and polyhedral to somewhat spindle-shaped. 

 Their nuclei are hypochromatic, have one to many nucleoli, are round to 

 nearly spindle-shaped, and vary in size. Mitoses are frequent. Some 

 mononuclear tumor giant cells are present. The cytoplasm is pale, eosino- 

 philic, and varies from a scant amount in the rounded cells to abundant in 

 the spindle-shaped epithelial tumor cells and in the polyhedral cells. The 

 stroma is usually represented by numerous, large and small, thin-walled 

 blood vessels with a small amount of connective tissue, except between large 

 nests of tumor cells where well defined septa of stromal connective tissue are 

 present. 



The rounded and spindle-shaped epithelial tumor cells can often be found 

 in the same high power fields. The latter can be seen arising from the 



