SPONTANEOUS HISTIOGENIC TUMORS OF EPIDIDYMIS OBSERVED IN B6C3F1 MICE

Four primary histiogenic tumors of the epididymis were discovered in 1 10 male B6C3F1 mice used in a carcinogenicity study in our laboratory. From the results, all these tumors were considered to be spontaneous. Histologically, the tumors were characterized by compact growth of sp indle to oval shaped histiocytic cells with or without a cleaved nucle us. Focal hemorrhage was present in three cases, and erythrophagocytos is occurred in such lesions. The tumors had some similar histological features of histiocytic sarcomas, which had been observed with high ma lignancy in other male and female animals. However, systemic growth an d atypism of neoplastic cells found in the histiocytic sarcomas were n ot observed in these epididymal tumors. On the other hand, four histio genic tumors of the uterus, with features characteristic of epididymal tumors, were observed in 106 female mice. The uterine histiogenic tum ors were regarded as benign or precursor lesions of histiocytic sarcom a. Furthermore, it is suspected that histiocytic sarcoma arises from t he epididymis.