A Case of Renal Mesenchymal Tumor in a Young Beagle Dog.

A 10-month-old male beagle dog had a renal mesenchymal tumor. The tumor tissue invaded into the adjacent renal tissue in an open-finger-like pattern, and entangled normal glomeruli and tubules. In most parts, the tumor mass showed a myxoid pattern around blood vessels, and in other small parts, a fascicular pattern. The tumor cells were spindle or oval in shape and had a densely basophilic nucleus and scant pale cytoplasm. Immunohistologically, the tumor cells were mostly positive for S-100 and myoglobin, and partially positive for Factor VIII reactions. These findings suggest that the tumor cells have an ability to differentiate into several kinds of mesenchymal cells.