Diagnostic data showing mesothelioma in a Virginia opossum from Wisconsin in 2025

Here, we present a unique case of an epithelioid mesothelioma with cutaneous metastasis in a Virginia opossum (Didelphis virginiana) from Wisconsin, USA. We performed a gross necropsy, histopathology, and immunohistochemistry. Significant gross findings included the absence of subcutaneous, visceral, peri-renal, and visceral adipose stores; subcutaneous edema; ascites; shaggy to nodular tan material on the surface of the abdominal wall, omentum, mesentery, liver, spleen, kidney, and adrenal glands; a 7.5 x 4 cm cutaneous mass on the left flank; and enlarged abdominal lymph nodes. Histopathology showed neoplastic mesothelial cells in the diaphragm, liver, kidney, adrenal gland, mesentery, omentum, lymph node, and skin. Neoplastic cells showed immunoreactivity with calretinin, Wilms tumor, cytokeratin AE1/AE3, and Vimentin V9.