Haemangiosarcoma (HSA) is an important malignant neoplasm of dogs that originates from vascular endothelial
cells. This study explored the suitability of using serum big endothelin-1 (ET-1) as a tumour
marker for canine spontaneous HSA. Serum big ET-1 was measured in dogs with splenic HSA (n = 14),
splenic malignant tumours other than HSA (n = 10), benign splenic lesions (n = 11) and normal healthy
dogs (n = 17) by ELISA. Serum big ET-1 levels in dogs with HSA were significantly (P < 0.01) higher than
in other dogs. High sensitivity (100%, 95% confidence interval 86–100%) and specificity (95%, 95% confidence
interval 86–95%) for HSA diagnosis were obtained using a cut-off of 17 pg/mL according to receiver
operating characteristic (ROC) curves (area under ROC curve 0.93). PPET1, ETA, VEGF and Hif1-α mRNA
expression, measured by real-time PCR, were elevated in HSA compared with normal tissues. These findings
suggest that elevated serum big ET-1 could be used as a diagnostic marker for canine HSA.