CARCINOMA OF THE THYROID IN SALMONOID FISHES. 399 



VISIBLE TUMOR STAGE — STRUCTURAL TYPES. 



In the larger tumors one finds a remarkable variation in the histologic picture. 

 The fundamental types may be divided into four — alveolar, papillar, tubular, and solid. 

 In occasional tumors one of these three types definitely predominates. In the 100 

 tumors selected for study these types occur in the following proportions: 



One is struck, however, in the study of these large infiltrating tumors, with the 

 remarkable variety of formation to be found in various regions. One may find in a 

 single tumor areas which may be placed under any one of the designations given. The 

 action of the stimulus upon the thyroid tissue in these tumors appears not only to work 

 irregularly, as will be shown by the advent of nodules of active proliferation and areas 

 simulating hyperplasia, but appears to throw the entire thyroid tissue into such a riot 

 of proliferation that a definite type for the entire tumor is seldom accomplished. The 

 epithelial cells forming the tumor present the greatest possible variety of form and size. 

 The nuclei are usually vesicular, in entire areas of a tumor the cells may present a typical 

 spindle form, thus simulating sarcoma, and in some instances areas of the tumor are 

 made up of a background of spindle cell tissue, through which are scattered small but 

 definite alveoli containing colloid. (Fig. 38.) 



In such a tumor we have a picture analogous to the so-called mixed tumor of the 

 thyroid encountered in man. Occasionally tumors may be met in which a large propor- 

 tion of the tumor is made up of large alveoli packed with solid masses of large cells, 

 deeply staining protoplasm and vesicular nuclei, and frequent karyokinetic figures, pre- 

 senting the picture of proliferating struma. (Langhans.) (Fig. 39.) 



Again, the general predominating type of a tumor may be distinctly papillary, in 

 which large vegetations covered with columnar epithelium and deeply stained nuclei 

 are found projecting into irregular spaces, usually free from colloid. The tendency 

 to papillary formation may be found in almost all of these tumors. Occasionally these 

 papilliform areas are of nodular form, in which case the cells forming the papillary nodule 

 are more deeply stained than the surrounding tubular or alveolar type, which gives 

 them a distinct focal character. (Fig. 45.) This marked tendency to focal or nodular 

 development within the tumors occasionally produces growths in which we have a large 

 mass of tubulo-alveolar structure, with nodules of solid, closely packed areas of intensive 

 proliferation. In figure 40 we have a low-power picture of such a tumor. The tumor 

 mass involves the entire area between the base of the tongue and the pericardial space and 

 extends between the arches to the floor of the mouth, where it projects in a series of 

 large protrusions, has pushed down the muscular structure of the isthmus, protrudes in 



