SPONTANEOUS NEOPLASMS IN MICE 185 



gland-like formations separated by thin septa of stroma with fairly large 

 blood spaces. Another may contain large irregularly shaped nests of closely 

 packed, poorly formed glands varying in size and lined by large and small 

 cuboidal epithelial tumor cells with numerous, small thin-walled blood 

 vessels and little stroma within the tumor nests but with dense stroma 

 separating them. A third type may exhibit pseudoglandular arrangements 

 of large and small, or fairly uniform size, imperfectly formed glands about a 

 focus or stroma which consists largely of a thin walled blood vessel, or about 

 a necrotic focus of tumor cells. Some are composed of clusters of large and 

 small, blood-filled endothelial lined spaces, surrounded by poorly formed 

 glands which may be markedly compressed by the blood spaces. Still other 

 types are seen where there may be metaplasia producing true epithelial pearl 

 formations with the stroma varying in amount and density. This descrip- 

 tion does not cover completely all the varieties which might be observed for 

 this tumor type. 



The distinguishing characteristics are some degree of attempted gland 

 formation by the majority of the epithelial tumor cells. The glands may 

 vary in size and arrangement and are lined by large or small cuboidal 

 epithelial cells. Gland walls vary from one to several layers in thickness and 

 show frequent loss of normal orientation of the cells where the walls have 

 become thickened. Mitoses are abundant. Infiltration of the surrounding 

 tissues and metastases to the lungs are often observed. 



Papillary cyst adenocarcinoma. — At least a large proportion of this group 

 arises in pre-existing papillary cyst adenomas. For this reason there is a 

 striking similarity in the general arrangement of the stroma in both the 

 benign and malignant tumors. However, in the latter the stroma is fre- 

 quently less abundant, except at the base of and within the central portion 

 of the papillary structure. The epithelial tumor cells cover the surfaces of 

 the poorly defined cysts and the branching papillae. On the latter they 

 often form irregular finger-like projections which contain a small amount of 

 connective tissue extending from the central stromal core (Fig. 98). In the 

 larger papillae the distal portions are composed chiefly of epithelial tumor 

 cells. These cells may be arranged in groups of gland-like formation, 

 nodules, sheets of cells or a combination of these with or without imperfectly 

 formed glands of different sizes. Even in the larger tumor masses thin 

 strands of stroma can be found in the form of scattered groups of small 

 connective tissue cells and small, thin-walled blood vessels. 



The epithelial tumor cells are medium sized, cuboidal or low columnar, 

 with oval, moderately hyperchromatic nuclei containing scattered chromatin 



