2o8 BIOLOGY OF THE LABORATORY MOUSE 



small, closely packed, spindle-shaped tumor cells and larger polyhedral 

 tumor cells. 



Mitotic figures are usually quite abundant in the spindle cells. Invasion 

 into the surrounding normal tissues is quite extensive. Metastasis to the 

 lungs has been observed in several cases and definite bone formation is seen 

 in the pulmonary metastases. 



When a sarcoma originating from bone shows definite cartilage formation 

 without newly formed bone, it is called a chondrosarcoma. The bone 

 sarcomas with some cartilage and considerable bone may be called chondro- 

 osteosarcomas. It is convenient, however, to call all malignant bone forming 

 tumors osteogenic sarcomas. 



Angio-endotheliomas. — These are malignant tumors that appear to have 

 arisen within some of the pre-existing benign hemangiomas and lymphangi- 

 omas due to the malignant changes which involved the endothelial cells. 

 Malignant changes produce sarcomas which are called hemangio-endotheli- 

 omas and lymphangio-endotheliomas respectively. 



In hemangio-cndothelioma the general architecture of the hemangioma is 

 evident. However, the endothelial cells are enlarged, rounded, vary in size 

 and have invaded much of the stroma. There are foci of solid masses of 

 cells in which the blood filled spaces have been obliterated. The cells have 

 rather deeply staining, finely granular, eosinophilic cytoplasm and moder- 

 ately hypochromatic oval nuclei. The nuclei contain many finely divided 

 chromatin granules. Mitoses are often abundant. Invasion of adjacent 

 normal tissues occurs and the simultaneous presence of this tumor in the leg 

 and spleen has been observed. Whether this is a case of multiple primaries 

 or metastasis is not easily determined. 



The lymphangio-endothelioma shows the same type of malignant endo- 

 thelial cells invading the stroma. These tumor cells also grow into the 

 endothelial lined spaces. Infiltration of adjacent normal tissues is seen. 

 Mitoses may be frequent. 



Tumors of the Lung 



There have been several publications (4, 20, 50 and 67) on tumors of the 

 lung, but probably the first was by Livingood in 1896 (36). 



The primary tumors of the lung are mainly those originating from the 

 lining cells of the bronchi and the alveoli. They may be classified as: 



1. Adenoma. 



2. Adenocarcinoma. 



J. Papillary adenocarcinoma. 



