I82 



BIOLOGY OF THE LABORATORY MOUSE 



fairly deep eosinophilic stain. Nuclei are elongated, narrow and blunt at 

 their ends with moderately pale, coarse and fine chromatin granules. 



These interlacing strands of large connective tissue cells vary in amount 

 in different fibro-adenomas, but they are always present. When they 

 definitely predominate over glandular parts, the tumor would then be called 

 an adenofibroma (Fig. 94). 



The capsule varies in thickness but not in direct relationship to the extent 

 of their fibrous parts. Mitoses are rare throughout the entire tumor. 



Adenocarcinomas of the Mammary Glands 



These tumors form a group of malignant neoplasms in which stromal 

 variations play a somewhat miner role in regard to diagnosis. However, the 

 mammary gland epithelium gives rise to epithelial tumor cells which may 

 assume a wide range of variations in arrangement and distribution within the 

 stroma without becoming so undifferentiated as to lose all trace of gland 

 origin. 



A high percentage of all the spontaneous tumors which have occurred in 

 the mice raised in our laboratory have been of mammary gland origin. 

 Most of these mammary gland tumors have been some form of adenocarci- 

 noma. The histological examination of these adenocarcinomas has shown 

 that some arose from pre-existing adenomas, and some appeared to have 

 developed directly from the mammary glands in the absence of adenomas. 

 When a large series of these mammary tumors is examined, a few characteris- 

 tic types emerge, each of which shows some variations and together they 

 cover the various forms of adenocarcinomas observed. The tumors are 

 classified according to the most outstanding cell arrangement. For example, 

 a papillary cyst adenocarcinoma may have a small focus of tumor cells 

 arranged as in intracanalicular adenocarcinoma or as in macroglandular 

 adenocarcinoma. 



Simple Adenocarcinoma. — This growth is composed of small, narrow 

 coiled ducts which are generally evenly distributed throughout the stroma. 

 These ducts are uniform in diameter, are about the size of the ducts of the 

 resting mammary gland and are lined by one to two layers of cuboidal 

 epithelial cells (Fig. 95). These cells are small, closely packed, possess a 

 scant amount of eosinophilic cytoplasm and oval, rather hyperchromatic, 

 nuclei. 



The duct-Hke structures are usually so closely packed that there is little 

 stroma between them, yet they may be spread through foci of loose stroma. 

 The tubules are generally so coiled that the majority of them are cut in cross 



