Primary Histiocytic Sarcoma of the Epididymis in B6c3f1 Mouse

A case of histiocytic sarcoma developed primarily in the epididymis of B6C3F1 mouse at 109 weeks old was reported. Metastases were observed in the liver and adipose tissue of the abdominal cavity. Tumor cells showed atypism, pleomorphism and active erythrophagocytosis. Touton type giant cells, which were PAS positive after diastase digestion, were seen in the tumor. Electronmicroscopically, the tumor cells had many slender processes forming interdigitation with the adjacent cells. However, no junctional complex or basal lamina was observed in the tumor cells. Tubular autolysozomes in the cytoplasm were characteristic feature of tumor cells of the present case. The vacuoles containing finger print membranes similar to the structures observed in human eosinophilic granuloma of the bone were found in some of the tumor cells. The structures similar to Birbeck's granule of the T-zone histiocyte were also observed. This case seems to be the first report on histiocytic sarcoma developed in the epididymis of B6C3F1 mice. Since fibrohistiocytic proliferative lesion developed in the epididymis of B6C3F1 mice. Since fibrohistiocytic proliferative lesions were known to develop occasionally in the epididymis of B6C3F1 mice, differential diagnosis from this proliferative lesions is important. Further immunohistological analysis for elucidating the origin and pathogenesis of this neoplastic lesion will be needed. (J Toxicol Pathol 7: 95•`102, 1994)