Fibrosarcomas in two rats arising from hepatic cysts of Cysticercus fasciolaris.

Two of five male Sprague-Dawley rats with hepatic tapeworm cysts developed large multinodular fibrosarcomas. Fibrosarcomas envelope tapeworm cysts, invaded the serosa of multiple organs, and extended through the diaphragm into the pleural cavity. Light microscopy, immunohistochemistry, and electron microscopy supported the diagnosis of fibrosarcoma. The parasites were identified as Cysticercus fasciolaris, the larval stage of Taenia taeniaeformis. The development of sarcomas in rats induced by Taenia sp. is thought to be attributable to the chronic inflammatory reaction of the capsule. There are parallels between these and other tumors occurring in mice and cats with suggested chronic inflammatory etiologies.