212 BIOLOGY OF THE LABORATORY MOUSE 



Carcinosarcoma. — This type may occur when the stromal connective 

 tissue of a lung carcinoma becomes malignant. We have seen it most 

 commonly in papillary adenocarcinomas. The sarcomatous part is com- 

 posed of rather large spindle cells irregularly arranged in interlacing strands. 

 Nuclei are spindle-shaped, darker than in the carcinoma, and the eosino- 

 philic cytoplasm appears to have longitudinal striations but no granules. 

 Mitotic figures are abundant. 



Primary tumors of the lung other than the above types are rare. How- 

 ever, the lung is a common site for metastases of carcinomas and sarcomas 

 from many other body regions (Fig. ii6). This is especially true of carci- 

 nomas in the mammary region which grossly may resemble carcinomas 

 primary in the lung. On histological examination a primary tumor of the 

 bronchi or alveoli can be identified as such by the characteristics of the 

 tumor cells. This includes their close resemblance to the normal lining cells 

 of the bronchi and alveoli in cell outline and staining properties. Primary 

 lung carcinoma cells are paler than mammary carcinoma cells and contain 

 fine eosinophilic cytoplasmic granules, as well as lobulated nuclei and multi- 

 nucleated cells which are not characteristic of the breast carcinomas. Other 

 types of pulmonary metastases that have been seen are from carcinoma of 

 the liver, malignant melanoma, osteogenic sarcoma, lymphocytoma, mono- 

 cytoma, etc. 



Tumors of the Blood Forming and Blood Destroying Tissues 

 (Round Cell Sarcomas) 



Enlargement of the mesenteric lymph nodes is not uncommon in old mice 

 from many of our stocks. Frequently this enlargement is benign and is 

 associated with some chronic infection. The usual finding in such cases is 

 lymph node hyperplasia. There is, however, a tendency for a small per- 

 centage of the mice from nearly all of the stocks to develop spontaneous 

 neoplasms of any of the lymph nodes, the spleen and sometimes the thymus. 

 Occasionally a tumor appears at a single focus, such as the mesenteric lymph 

 node. When the axillary and inguinal lymph nodes are involved, there is 

 usually a bilateral enlargement of these glands as well as of the cervical 

 lymph nodes. The spleen and internal lymph nodes may or may not 

 become enlarged when bilateral enlargement of the subcutaneous lymph 

 nodes occurs. 



Mice with neoplasms involving the spleen and lymph nodes do not 

 usually live long after the symptoms become marked. The outstanding 

 gross characteristics are signs of ill health, such as dull, rough coat and 



