Expression of Oxytocin Receptors in Canine Mammary Tumours.

The aims of the present study were: (1) to investigate the presence of oxytocin receptors in benign and malignant canine mammary tumours (CMTs) and to evaluate the possible association between oxytocin receptor (OTR) expression and the expression of oestrogen receptor (OR) α and ORβ, and (2) to examine associations between receptor expression and tumour size, clinical stage, histological subtype, tumour grading and lymph node status. Forty-three canine mammary tumour samples (19 benign, 24 malignant) were examined by immunohistochemistry to detect OTR, ORα and ORβ expression. Results were expressed as total score for each receptor, calculated as the sum of the percentage of positive cells and the intensity of immunolabelling. In all of the evaluated mammary tumour samples, OTRs were identified and their expression tended to be higher in benign tumours than malignant tumours. Among the malignant tumours, the expression of OTR was significantly higher in grade I and II lesions than in grade III lesions. ORα-positive tumours had a tendency towards a higher OTR total score than ORα-negative tumours. These results report for the first time that CMTs express OTRs and their expression is associated with the presence of ORα. An interaction between oxytocin and the OTR might play a role in the development and progression of this type of neoplasia.