Postmortem Detection of Blood Vascular Tumour-Cell Emboli in 31 Dogs: Macroscopic and Histological Findings.

Despite the high prevalence of neoplastic diseases in dogs, tumour-cell embolism is poorly documented. This study aimed to characterise the presence and pathological features of distant blood vascular tumour-cell emboli (TCE) in dogs submitted for necropsy. TCE were histologically confirmed in 31/528 dogs (5.9%) that died or were euthanized due to neoplastic disease, most frequently mammary carcinomas (17/31, 54.8%). In 15/31 dogs (48.4%), TCE were associated with secondary macroscopic lesions, such as haemorrhage, whereas in 16/31 dogs (51.6%), there was no clear association with additional pathological changes. TCE were most commonly observed in the lungs (25/31), kidneys (9/31), adrenals (5/31), brain (5/31), and myocardium (5/31). Macroscopic pulmonary changes included petechiae or suffusions (8/31), and TCE-associated haemorrhages were also observed in the myocardium (4/31), kidneys (2/31), adrenals (2/31), brain (2/31), and gastrointestinal serosae (2/31). Histological lesions associated with TCE included haemorrhage (18/31), thrombosis (11/31), oedema (8/31), infarcts (7/31), and intimal proliferation and perivascular fibrosis (4/31). Taken together, these findings suggest that blood vascular TCE may be more prevalent in dogs than currently recognised and reinforce the importance of careful pathological evaluation for their detection. The clinical, macroscopic, and microscopic features described herein provide a practical framework for recognising TCE in veterinary pathology and underscore the need for further studies addressing their pathogenesis, clinical significance, and impact on disease progression in dogs.