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Although canine mammary tumours (CMT) are the most common malignant tumours in bitches the pathogenesis is far from understood. To analyse the role of the transforming growth factor β (TGFβ) family in the carcinogenesis of CMT, relative mRNA and protein expression of TGFβ-1, -2 and -3, TGFβ receptor (TGFβR)-1 and -3, latent TGFβ-binding protein (LTBP)-1, -3 and -4, and oestrogen receptor α in CMT were quantified. mRNA expression concentrations were measured in laser-microdissected tissue samples of mammary adenomas, carcinomas and their lymph node metastases and normalised to the non-neoplastic mammary gland of the same dog. Carcinomas and metastases had significantly decreased expression levels of TGFβ-3, TGFβR-3 and LTBP-4, but increased LTBP-1 expression when compared to non-neoplastic glands or adenomas. Decreased TGFβ and LTBP-4 expression were confirmed immunohistochemically. The data suggested that loss of TGFβ-3 and LTBP-4 may have growth-stimulatory effects in late-stage tumours, and loss of their expression, together with reduced TGFβR-3 expression, may be associated with increased proliferative activity of CMT similar to findings in human breast cancer.