TUMORS. 



391 



3. Epithelioma. This tumor is essentially a carcinoma springing 

 from stratified epithelium. Under normal circumstances the cells 

 of this variety of epithelium multiply in its deeper layers and are 

 gradually pushed toward the surface while they mature. Epithe- 

 liomata are produced when the proliferating cells penetrate the 

 underlying tissues in columns, which ramify through those tissues 

 and ultimately appear as the contents of well-defined alveoli sur- 

 rounded by a fibrous-tissue stroma similar to that present in car- 

 cinomata (Fig. 359). The epithelium retains its general characters : 

 the cells at the periphery of the alveoli multiply, and either further 



FIG. 360. 



Epithelial pearl-body from an epithelioma of the lip : a, pearl-body ; 6, surrounding epithe- 

 lium, forming one of the epitheliomatous tongues or columns; c, round-cell infiltra- 

 tion of the contiguous fibrous tissue. 



infiltrate the surrounding tissues or crowd each other toward the 

 centres of the alveoli as they increase in number and size. Here 

 they eventually undergo keratoid transformation, just as they would 

 upon the surface of the normal epithelium ; only here they are 

 crowded toward the centres of the alveoli, where the horny scales 

 become imbricated to form globular masses, called epithelial " pearl- 

 bodies " (Fig. 360). The epitheliomata may penetrate into the 

 lymphatics and be subject to metastasis in a manner entirely com- 

 parable to that already described above. They are, therefore, 

 malignant, though of slower growth than the medullary or simple 

 carcinomata, at least during the early stages of their development. 

 It should always be borne in mind, when considering the prog- 



