2IO BIOLOGY OF THE LABORATORY MOUSE 



Here the tumor consists of poorly formed, gland-like structures scattered 

 through nests of irregularly arranged tumor cells. These cells vary from 

 polyhedral to columnar, possess hypochromatic nuclei and abundant cyto- 

 plasm filled with fine eosinophilic granules which are similar to those of the 

 epithelium of the bronchi. The stroma consists principally of thin-walled 

 blood vessels. Mitoses are frequent. Metastases in the liver have been 

 observed. 



Papillary adenocarcinoma of the lung. — This type may be seen as definite 

 masses within, or continuous with, the more benign adenomatous form dis- 

 cussed above, and apparently arises through malignant changes. This type 

 of carcinoma may also be in direct continuity with one of the smaller bronchi. 

 The papillary type of growth is by far the most commonly seen among our 

 carcinomas of the lungs of mice. Even tiny masses show it as definitely as 

 the large tumors, which may involve an entire lobe of the lung. The archi- 

 tecture shows closely packed, branching and anastomosing, thin, finger- 

 like strands with a stromal core of capillaries and a varying amount, usually 

 small, of connective tissue stromal cells (Fig. ii6). The papillary adeno- 

 carcinomas are darker staining than the benign type, have more cells, many 

 of which are larger and show piling up to form several cell layers at many 

 foci on the papillae. The tumor masses are chiefly composed of papillary 

 structures without cyst formation. Occasionally one can observe dense foci 

 of connective tissue stroma from which several of the papillary growths 

 extend to form the main tumor mass. The stroma in the bulk of the tumor 

 is often scant. The tumor cells of papillary adenocarcinomas vary in size 

 and shape. Eosinophilic cytoplasmic granules are prominent, nuclei are 

 hypochromatic and vary in size and shape, with some multilobulated, 

 bilobed and binucleated forms present. In some tumors, foci of columnar 

 tumor cells show well developed goblet cells. A few tumors may exhibit one 

 to several layers of epithelial tumor cells lining intercommunicating spaces 

 with only thin strands of stroma between them. Into these spaces project 

 short, branching papillae giving an irregular appearance to the lining. On 

 cross section these structures appear as large glands, not as cysts, presenting 

 frequent foci of ciliated columnar epithelial tumor cells. These are located 

 between the more piled up foci of tumor cells. 



Papillary adenocarcinomas are often found close to the smaller bronchi, 

 and it is not uncommon for these tumors to extend into these bronchi, nearly 

 occluding them. 



Carcinoma simplex. — This may originate in a papillary adenocarcinoma 

 and often appears as closely packed cells arranged in an irregular pattern. 



