Ito cell tumor: Immunohistochemical investigations of a rare lesion in theliver of mice

In 2 lifespan transgeneration experiments using a total of 4,682 CBA/J mice , we observed uncommon lipomatous lesions in the livers of 8 mice independe nt of the treatment. Macroscopically, the lesions were described as pale wh ite areas (2) or nodules (6) during necropsy. The lesions ranged from 1 to 15 mm in diameter. Microscopically, the lesions consisted of nodular aggreg ations of round to spindle-shaped cells that partly caused distinct compres sion of the adjacent hepatic parenchyma. The tumor cells were smaller than hepatocytes and had dark oval nuclei. Many of the more spherical cells cont ained clear vacuoles of various sizes, which were shown to be Lipid droplet s by oil red O staining. In addition to Gomori's silver and Masson's trichr ome staining, several immunohisto-chemical stains were used to characterize the origin of the proliferating cells. Tumor cells were labeled by vimenti n, actin, desmin, and proliferating cell nuclear antigen. The 2 cell phenot ypes showed similar staining characteristics. Increased amounts of laminin and tenascin, 2 extracellular matrix proteins of the liver, were detected w ithin these neoplasms. Summarizing, we suggest that these tumors are of Ito cell origin.