Desmin expression by a gastrointestinal stromal tumor in a dog

This report describes the histological and immunohistochemical features of a small intestinal tumor that resembled a human gastrointestinal stromal tumor (GISTs) in a seven-year-old male cross-breed dog. This was unique because of the expression of desmin by the tumor. Grossly, the white-gray tumor measured 8.0 × 4.0 × 6.5 cm and was 760 gram in weight. It was cystic and enveloped the jejunum. Histopathologically, long spindle-shaped cells were arranged densely in the interwoven pattern. The tumor cells had a low rate of mitosis, were pleomorphic, and were positive for vimentin, ?-smooth muscle actin, desmin, S100 and C-KIT and negative for CD34 on immunohistochemistry. The expression of desmin in the cytoplasm of this tumor cells is a rare event in these types of tumors.