SPONTANEOUS NEOPLASMS IN MICE 



197 



pale, oval frequently pyknotic, nuclei. The cytoplasm is abundant, 

 acidophilic and often contains coarse keratohyalin granules. These cells 

 grade over into smaller, closely packed, disorderly, polyhedral to somewhat 

 spindle-shaped cells. They possess a relatively small amount of eosinophilic 

 cytoplasm and contain oval, moderately hypochromatic nuclei with scattered 

 coarse chromatin granules. Scattered foci of brown pigment resembling 

 melanin are often seen. Mitoses are frequent in these smaller cells. 



Epithelial pearl 



YiG. 105. — Epidermoid carcinoma from the lip of a female mouse. A, tumor invad- 

 ing dermis around vibrissa (X200); B, cellular detail of this same tumor (X400). 



Occasionally a very malignant form shows little epithelial pearl formation 

 (Fig. 107). It may consist of wildly growing spindle-shaped epithelial 

 tumor cells that blend with narrow strands and small nests of the smaller 

 types of polyhedral epithelial tumor cells (Fig. 108B). Unless the origin can 

 be traced to the epidermis in this type of tumor, the architecture is so mis- 

 leading that it could confuse one in interpreting the histopathology . ]\Iitoses 

 are abundant. 



Carcinomas of skin appendages. — These all give the same general picture. 

 They originate in the specialized sebaceous glands of the head region of 



