Histiocytic sarcoma in Wistar rats. A light microscopic, immunohistochemical, and ultrastructural study.

Histiocytic sarcoma, a recently described tumor entity in rats, was studied by light microscopy in 20 male and female Wistar rats. The tumors originated from subcutaneous tissues; metastasis involved primarily the liver with sinusoidal spread and the lungs with peribronchiolar distribution. The characteristic features of this tumor were the uniform population of tumor cells, palisading necrosis, and abundant multinucleated giant cells. Immunocytochemical and ultrastructural findings confirmed the histiocytic nature of the tumor cells.