SPONTANEOUS NEOPLASMS IN MICE 



217 



Myeloid Cell Tumors 

 Most myeloid cells are immature 



Erythrogenic foci are absent among 

 myeloid cells 



Megakaryocytes are few and present 

 only in the organs (the spleen, liver 

 and lymph nodes) where they are 

 found in non-leukemic conditions 



Myeloid cells often invade muscle and 

 other non-hematopoietic tissues 



Blood usually contains immature mye- 

 loid cells 



Liver is usually enlarged and gray- 

 brown 



Most of the lymph nodes are usually 

 enlarged 



Hemorrhages are frequent in viscera 

 (lungs, lymph nodes, etc.) 



Transmissible to other mice 



Not shown to be produced by bacteria 



Non-Malignant Extramedullary 



Myelopoiesis 



All stages of development of myeloid 



cells are present 

 Erythrogenic foci are usually present 



Megakaryocytes are usually numerous 



Cells are non-invasive 



Blood is normal or there is leukocy- 

 toses with numerous mature forms 



Liver is usually not enlarged and is 

 brown-red 



Most of the lymph nodes are usually 

 of normal size 



Hemorrhagic manifestations are ab- 

 sent 



Not yet shown to be transmissible 



Can be produced by bacteria 



Myelocytoma. — This is a tumor made up of immature myeloid cells. 

 The predominating tumor cells may be myeloblasts or different kinds of 

 immature granulocytes (Fig. 118). There may be considerable variation 

 between the cells of different tumors, but the cells have a tendency to be 

 rather uniform in individual cases. Variations in size and staining power of 

 these tumor cells indicate an approach to the sarcoma type. Myelocytoma 

 may be leukemic or aleukemic. Mitoses may be fairly frequent and inva- 

 sion into adjacent normal tissues occurs. 



Myelosarcoma. — This is similar to myelocytoma, except that the cells 

 are more variable in size and assume bizarre shapes. Mitoses are frequent. 

 Extensive infiltrations into normal tissues may occur. 



Monocyte Tumors (Monocytoma or Histiocytoma*) 



These tumors are rare in many stocks of mice. However, Tyzzer (67) 

 and Slye (51) report cases, without diagnoses, which from their pictures and 

 descriptions appear to be similar to a type of tumor (probably monocytoma) 



* (The neoplasms sometimes called reticulum cell tumors probably belong in this 

 group.) 



