Spontaneous salivary gland tumors in rats are rare. The authors report a poorly differentiated carcinoma of a submandibular gland in a ten-week-old rat that was positive for vimentin. Microscopically, the neoplastic cells showed a diffuse growth pattern in most areas of the tumor mass and a nestlike structure in a part of the peripheral area. Immunohistochemically, the cells were positive for keratin and vimentin but not for a-smooth muscle actin. Ultrastructurally, desmosome-like structures were observed. Based on these findings, the tumor was diagnosed as a poorly differentiated carcinoma. The origin of the neoplastic cells would be either acinar or ductal cells. This suggests that acinar or ductal cells have the potential to transform into vimentin-expressing cells.

Abstract:In a young adult (8 weeks old) Sprague-Dawley (SD) rat, a 7 mm-diameter hemispherical nodule with white spots was macroscopically identified on the visceral surface of the spleen. Microscopically, the nodule consisted of areas of enlarged white pulp. The periarteriolar lymphoid sheaths (PALS) area was expanded due to an increase in lymphocytes, but the marginal zone was relatively atrophied. Although minimal compressions and mitotic figures were sporadically observed, there were no structural alterations or atypical cells. Immunohistochemically, there were increased numbers of proliferating cells (Ki-67 positive cells) in the PALS and red pulp areas. In the PALS area, there were increased numbers of T-cells and macrophage/dendritic cells, while in the red pulp area, there were increased numbers of T-cells and B-cell/plasma cells. This lesion, which is believed to be hyperplastic and not neoplastic, was diagnosed as lymphoid hyperplasia, a condition considered to be uncommon in young adult SD rats. (J Toxicol Pathol 2008; 21: 243-247)