304 TUMORS. 



NERVE-TISSUE TYPE NEUROMATA. 



VASCULAR-TISSUE TYPE ANGIOMATA. 



Normal Tissue. Tumors. 



Blood-vessels. Angioma. ^ 



Lymph- vessels. Lymphangioma. 



EPITHELIAL-TISSUE TYPE. 



Normal Tissue. Tumors. 



Glands. Adenoma. S 



Various forms of epithelial cells Carcinoma, ^ 



and associated tissues. 



Tumors Formed by Various Combinations of Tissue Types 

 Mixed Tumors. 



In a considerable proportion of tumors more than one type of tissue 

 is present, and it is customary to indicate this by compound names, such 

 as osteo-sarcoma, adeno-carcinoma, etc. Discrimination is necessary in the 

 use of such names, however, and one should be clear as to what he 

 wishes to express in this way. All tumors have a certain amount of 

 fibrous stroina which carries the blood-vessels and forms a sustaining 

 framework. In the early stages of tumor growth this matrix may be the 

 tissue in which the tumor starts, which is either not increased in amount 

 or is hyperplastic. Thus in carcinoma of the stomach, the stroma may 

 be fibrous in the mucosa or composed of smooth muscle if the stomach 

 wall be involved ; but such growths would not be called either fibro- 

 carciuoma or myo-carciuoma. It is only when the new tissue assumes 

 the characters of an independent growth that it can be justly indicated 

 in the compound name. This may not be easy or always possible to de- 

 termine, but the desirability of doing so should be held constantly in 

 mind. Unfortunately the compound name is by some writers used to 

 indicate simply the seat of a tumor growth ; in this sense osteo-sarcoma 

 means simply sarcoma of the bone and not an association of osteoma and 

 sarcoma. 



It should also be remembered in this connection that a tumor of 

 mixed type does not always, perhaps not often, start as such, but may 

 assume this character by metaplasia within the limits of a tissue group. 

 Thus the establishment in fibroma of bone or cartilage growth and the 

 assumption by the adenomata of the carcinomatous type are common. 

 Furthermore, although these mixed forms of tumors may arise second- 

 arily by metaplasia, the more or less distinct forms of tissue may finally 

 become so independent of one another that some of the metastases from 

 such a mixed tumor may show only one tissue type. The possibilities 

 in tissue metaplasia should be taken into the account before assuming, 



