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To investigate the relationship between the expression of the PTEN (phosphatase and tensin homolog deleted on chromosometen) and VEGF (vascular endothelial growth factor) and the clinicopathological features in canine mammary gland tumours, the expression levels of PTEN and VEGF protein were assessed in 50 cases of canine mammary gland tumours tissues and 4 cases of normal mammary gland tissues with using immunohistochemical method. The over-expression rate of PTEN protein was 100% in normal and well-differentiated mammary gland tissues and 67% in breast cancer cases respectively with a significant difference between the two groups (P < 0.01). Expression of PTEN was not related to age and tumour size, but closely correlated to lymph node metastasis (P < 0.01). The over-expression rate of VEGF protein was 33.3% in normal mammary gland tissues, and 78% in canine mammary gland tumours with a significant difference between the two groups (P < 0.01). Expression of VEGF was not related to age or tumour size, but closely correlated with lymph node metastasis and clinical stage (P < 0.05). Therefore the combination detection of PTEN and VEGF could serve as an important index to estimate the biological behavior and prognosis of canine mammary gland tumours. Reduced expression of PTEN might be involved in carcinogenesis and progression of canine breast cancer by up-regulating the VEGF expression to enhance angiogenesis.