That the histological appearance of the cells predominating, in this tumor are compatible with plasma cells has ample evidences. Another characteristic feature of this tumor is its slow proliferation as was shown in the result of the transplantation experiment. In view of these two features this tumor may be concluded to be a neoplasm derived from a blood cell type with proliferation not leukemic, but simulating sarcoma of fairly mild malignancy. For these reasons the author designates this tumor as "plasma cell sarcoma" or "extramedullar plasmoma."
Supravital appearance of the mitochondria in the plasma cell myeloma of man was reported by Fukase (1949). In comparison with the reported appearance, the author's tumor appeared more sarcomatous in that it contained smaller, but more numerous mitochondria. Since Yoshida sarcoma is now accepted as a monocyte-sarcoma, so is the author's tumor compatible with a plasma cell sarcoma. It is regretted that this tumor died out after 7 generations. There must have been some means to preserve the strain of this tumor, since Furth successfully transplanted leukemia of mouse serially for many generations of inbred strain.
It deserves attention that this tumor arose primarily in the subcutaneous tissue exposed to the repeated doses of monoiodoacetic acid and in the absence of bone marrow involvement. This fact sharply contrasts to the fact that most plasma cell tumors in man are derived from the bone marrow in the form of a myeloma with the exception of a plasma cell sarcoma reported by Maresch (1909) to have invaded lymph glands systematically, and a non-myelogenic plasma cell sarcoma arising primarily in the connective tissue of the neck (Kagamiyama, unpublished data).
Since plasma cell derives its origin from the adventitia cells around the blood vessel (Amano, et al, 1944), plasma cell sarcoma arising primarily from tissues other than bone marrow is no surprising matter. It is rather strange that plasma cell sarcoma like this is considered to be so rare.
Plasma cell myeloma of man is classified into γ-globulin type and β-globulin. type. The author performed assays of globulin fraction, both qualitative and quantitative, on this tumor. With a cooperation of Dr. Hanaoka the author examined blood samples obtained from tumor-bearing animals of the 2nd generation on the 15th post-plantation day for their protein fractions electrophoretically. There was no evidence of increasing globulin fraction. The author does not intend to generalize this fact on the entire strains of the inducedtumor, since the tumor-bearing-animals used in this assay had received repeated doses of antibiotics in order to subdue the superimposing mixed infection and the tumor itself was regressing at the time of this assay. After the 4th generation tumor regained its vigor, but no electrophoretical analysis of the protein fractions was made either on blood or the tumor extracts.
That hybrid strains were used in this study constituted the primary reason for the author's failure to transplant this tumor for many generations. Another experiment is being contemplated employing inbred strain of animal. During the course of this study occasional cysticercus sarcoma (reticulosarcoma) of the liver occurred. This tumor could be transplanted from many generations without any particular difficulty, contrasting sharply to the failure of the plasma cell sarcoma to be carried beyond 7 generations despite the best caution employed by the author. In this failure the highly differentiated character of the tumor cell-a blood cell type-probably plays a part. With this failure, this study still merits a publication, since occurrence of plasma cell sarcoma has not reported on.
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