A Spontaneously Occurring Renal Tubule Carcinoma in a Mouse

Spontaneous occurrence of renal tubule carcinoma in mice is known to be rare. The following features of this tumor are recognized as areas of hemorrhage and massive necrosis and many show atypical cells and numerous mitotic figures. The present renal tubule carcinoma developed in an untreated B6C3F1 male mouse at the age of 109 weeks. The tumor mass occupied nearly the entire renal cortex and invasion of normal renal tissue was observed. The tumor had solid cell nests, a gland-like structure, definite neovascularization and capsular invasion. The tumor cells had clear eosinophilic cytoplasm, a brush border structure and high proliferative activity. Although tumors derived from the proximal tubule reportedly show basophilic cytoplasm, the tumor cells in this mouse had clear eosinophilic cytoplasm. Consequently, the animal was diagnosed as having an unusual renal tubule carcinoma (classification: solid type). (J Toxicol Pathol 2007; 20: 253-256)