An atypical case of histiocytic sarcoma in a Wistar rat (Rattus norvegicus).

Histiocytic sarcoma is the most frequent hematopoietic tumor in rats. We report here a histiocytic sarcoma infiltrating the liver, the spleen and the pancreas from a Wistar rat. In the liver, the tumor was associated with oval cell and bile duct hyperplasia. The cells looked like neoplastic histocytic cells described in this species but with some particularities (e.g. lack of multinucleated giant cells). At immunohistochemistry, neoplastic cells in the liver were vimentine positive but lysozyme and CD68 negative. In the kidney, lysozyme-positive cytoplasmic droplets were observed. We describe here an atypical case of histiocytic sarcoma in the rat and we compare the nature of these neoplastic cells to other species.