Malignant mesothelioma in a seven-week-old puppy.

A case of diffuse malignant peritoneal mesothelioma in a 7-week-old puppy is reported. The puppy presented with a recurrent abdominal effusion. An exploratory laparotomy revealed extensive adhesions. Necropsy findings included pleural thickening, and enlargement of the renal and anterior mediastinal lymph nodes. The microscopic features were typical of primary desmoplastic diffuse mesothelioma of the peritoneum and pleura with secondary lymph node metastasis (renal and anterior mediastinal). The tumour was classified as epithelial in type. The extent of the tumour and the distant metastasis were considered to reflect a high degree of malignancy. A congenital origin was suspected.