Transmissible venereal tumour with encephalic metastasis in dogs.

From January 2000 to December 2023 the Laboratory of Animal Pathology of the Federal University of Campina Grande received 6,218 canine autopsy and biopsy submissions, with six (0.09%) autopsy cases diagnosed as transmissible venereal tumour (TVT) with encephalic metastases. The mean age of affected dogs (four females and two males) was 7 years. Dogs were all from urban areas and were either semidomiciled (four cases) or stray (two cases). Clinical findings consisted of multilobular, ulcerated masses affecting the genital area (five cases) or skin (one case). Neurological signs were reported in three cases and included lethargy, seizures and ataxia. Grossly, encephalic metastases were subdural and extraparenchymal and affected the telencephalic hemispheres (four cases) or the base of the brain (two cases). In all cases, histology revealed a round cell neoplasm arranged in sheets supported by a scant fibrovascular stroma. In the brain, tumours often compressed and occasionally infiltrated the surrounding neuroparenchyma. Neoplastic cells had immunolabelling for vimentin, CD45RA, Iba1 and lysozyme, and no immunolabelling for MHC class II, CD117, CD3, CD79 and MUM1. Encephalic metastases of TVT should be included in the differential diagnosis of nervous system diseases of dogs in endemic areas where TVT is diagnosed in genital or extragenital tissues.